This section proposes the simplest scheme for finding out the causes of malfunctions and failures occurring in the components and systems of the vehicle. Failures and their possible causes are divided into groups based on their relationship to certain components or vehicle systems, such as engine, cooling system, etc., in addition, the text provides links to chapters and sections related to these problems.
Remember that successfully completing a root cause troubleshooting is not black magic reserved for experienced professional mechanics, but is determined by a combination of specific knowledge and a patient, systematic approach to investigating the problem. You should always move from simple to complex, bring each check to its logical conclusion and try not to miss obvious facts - anyone can forget to fill the fuel tank or leave lights on at night.
Finally, you should always try to get a clear picture of the development of the malfunction and take appropriate steps to prevent recurrence. If the failure of the electrical equipment occurred due to a violation of the quality of the contact, check at the same time the condition of all other contacts and electrical connectors of the system. If the same fuse continues to blow several times in a row, there is no point in replacing it further - you must try to find out the cause of the failure. Remember that the failure of a minor component may be a sign of a malfunction of a more important node or the entire system.
Engine
If the engine does not start, you should try to calmly analyze the situation.
Petrol models
Mandatory conditions for starting any gasoline engine are the correct supply of the air-fuel mixture to the cylinders and the adequacy of sparking on the spark plugs.
First of all, you should make sure that the fuel supply is working properly.
To determine if a spark is being produced, the candles should be unscrewed, inserted into the tips and individually applied to the mass. In this case, do not hold the wire or tip with your hands - use insulated pliers. Have an assistant start the engine. If there is no spark, try to determine the cause of the failure.
Procedures for diagnosing the electronic control system and fault codes are also given in Chapter Engine Electrical Systems (see Sections Ignition and injection control system checks, Troubleshooting - general information and preliminary checks, Checking and adjusting the ignition timing and Specifications).
Diesel models
Among the conditions, the fulfillment of which guarantees the successful start of any diesel engine include:
- Sufficient to start the speed of the crankshaft of the engine;
- Temperature of compressed air in combustion chambers sufficient for self-ignition of fuel; those. achievement of the specified compression pressure and, when starting in cold weather, the correct functioning of the glow plugs;
- Injection of finely dispersed fuel into the combustion chambers at exactly the right moment.
First of all, you should make sure that the starter is in good condition, then check the fuel supply, nozzles and the operation of the pre-glow. A description of the procedure for checking the condition of glow plugs is given in Section Checking glow plugs.
Engine won't crank when trying to start it
1. The battery terminals are corroded or the wire ends are loose.
2. Discharged or defective battery. If the wire lugs are not oxidized and are securely attached to the battery terminals, turn the key "ignition" to the ON position, then turn on the headlights and/or windshield wipers - if they do not work, the battery is low.
3. Transmission is not correctly set in position "R".
4. The wiring in the starting system circuit is broken or the wires are loose on the terminals.
5. The starter gear is stuck in the ring gear of the drive disc.
6. Defective starter relay.
7. Faulty starter.
8. Faulty ignition switch.
Engine cranks but won't start
Petrol models
1. Wrong start. Proceed as follows:
- Engage the parking brake;
- Engage neutral (RKPP) / move the selector lever to position «R» or «N» (AT);
- Without depressing the gas pedal, turn the key in the ignition switch to the right until it stops. Release the key as soon as the engine starts. If a warm engine cannot be started by cranking it with the starter for more than 4 seconds, slowly depress the gas pedal. Do not crank the engine for more than 30 seconds in a row, wait at least 15 seconds before trying again;
- At unstable speeds (e.g. misfires) in order to avoid damage to the catalytic converter, try to turn on the engine only for a short time and do not allow heavy loads, - immediately drive the car to a Mercedes-Benz service station;
- In areas where the outside temperature often drops below -20°C, the installation of a coolant heater is recommended - a certificate on this issue can be obtained from any Mercedes-Benz service station.
2. Faulty or disabled engine immobilizer.
3. The fuse of the electric fuel pump or electronic injection system is faulty.
4. The fuel tank is empty or filled with low-quality fuel.
5. The air filter is very dirty. There are vacuum leaks in the air supply elements, malfunctions in the fuel injection and ignition control system.
6. Low battery (engine cranks too slowly).
7. The battery terminal connections are oxidized or loose.
8. The fuel pump is faulty, or its relay is damaged - check by ear that the pump is activated when the ignition is turned on.
9. Damaged or excessively wet components of the ignition system.
10. Worn or defective spark plugs, or incorrect spark plug gap.
11. The electrical wiring of the starting system is broken or disconnected, or the fastening of the wires to the terminals is loose.
12. The electrical wiring of the ignition coil is broken or disconnected, or the fastening of the wires at the coil terminals is loose.
13. The fuse of the engine control unit is damaged, any of the sensors is faulty: Hall, impulse sensor, coolant temperature sensor (ECT) or intake air (IAT).
14. Insufficient compression pressure.
Diesel models
Note. Make sure that during the operation of the pre-glow system (control lamp on) all onboard electrical consumers (light, heated rear window, radio, etc.) were disabled.
1. Wrong start. Proceed as follows:
With a cold engine and outside air temperature below +5°C:
- Set the parking brake, depress the clutch pedal;
- On models with AT, move the selector lever to the position "R" or "N". turn the key «ignition» to position 2 and wait for the preheat indicator lamp to turn off. As soon as the lamp goes out, start the engine without depressing the gas pedal;
- If intermittent flashes first occur, continue cranking the starter until the engine RPM stabilizes (but not more than 30 seconds continuously);
- If starting fails, try again after half a minute, proceeding in the manner described above.
When the outside air temperature is above +5°C there is no need to preheat the engine. This also applies to starting an already warm engine in colder weather. Do not press the gas pedal.
2. Faulty engine immobilizer.
3. The fuse of the electric fuel pump or the preheat system is defective.
4. The engine is not warmed up: check the correct functioning of the preheater.
5. There is no voltage at the solenoid shut-off valve. Connect a voltmeter or an LED probe to the switch. Turn on the ignition, the LED should light up, otherwise you need to find a break in the wiring and fix it.
6. Faulty solenoid shut-off valve. Check the reliability of the fastening of the electromagnetic switch, evaluate the condition of the contacts. Turn the ignition on and off, the switch should click.
7. There is damage in the fuel supply lines, or air has entered the latter:
- Pipelines or hoses are mechanically damaged or clogged, - clean the fuel pipes and remove air from the lines and the filter;
- The fuel filter is clogged, - replace the filter element;
- In winter, you should check the filter and pipelines for the presence of ice or wax, - drive the car into a heated garage, add gasoline to the system;
- Clogged tank vent or fuel intake strainer - clean.
8. The adjustment of the moment of the start of the fuel supply is knocked down.
9. Injectors are faulty, - when the union nut of the fuel line of the faulty injector is loosened, the engine speed will not drop.
10. Faulty high pressure fuel pump (injection pump).
11. Insufficient compression pressure.
The starter operates without cranking the engine
1. Stuck starter gear.
2. Worn or damaged starter gear teeth or flywheel crown.
Difficulty starting a cold engine
1. Discharged or insufficiently charged battery.
2. There is a malfunction of the functioning of the components of the power system, or electrical equipment.
3. There is a deposition of paraffin in the fuel fine filter.
4. Faulty diesel engine glow plugs.
Difficulty starting a hot engine
Refer also to Section Hot engine does not start.
1. The patency of the air filter is broken.
2. There is a malfunction of the functioning of the components of the power system, or electrical equipment.
3. Fuel is not supplied to the injectors of the injection system.
4. The fuel advance angle of the diesel engine has gone astray.
5. There is not enough compression pressure in the cylinders, the injection pump of the diesel engine is faulty, or its adjustment is violated.
Starter engagement is too noisy or difficult
1. Worn or damaged starter gear teeth or flywheel crown.
2. Lost starter mounting bolts, or weakened their tightening force.
Engine starts but immediately stalls
1. Faulty engine immobilizer.
2. Faulty wiring, or loose wires at the coil or generator terminals.
3. There is a malfunction of the functioning of the components of the power system or electrical equipment.
4. The basic settings of the engine control module are violated (ECM).
5. There is damage in the exhaust system/catalytic converter.
6. Vacuum loss occurs at the throttle body, intake manifold, or through the vacuum hoses.
The stability of the engine at idle is broken
Petrol models
1. There are vacuum losses. Make sure that the fixing bolts/nuts are securely tightened, check the fact and quality of fastening on your fittings on the inlet pipeline of all vacuum hoses. Listen to the running engine with a stethoscope or a piece of fuel hose. The presence of a hissing sound will reveal the source "leaks" vacuum, - no less effectively you can use a solution of soapy water to check.
2. There is a malfunction of the functioning of the components of the power system or electrical equipment.
3. The patency of the valve of the controlled crankcase ventilation system is disturbed.
4. The patency of the air filter is broken.
5. The fuel pump does not supply enough fuel to the injectors of the injection system.
6. There are leaks through the cylinder head gasket - measure the compression pressure in the engine cylinders (see chapter Engine).
7. Camshaft lobes worn out.
Diesel models
1. The quality of the connections of the fuel hoses on the injection pump and the fuel filter is broken.
2. Mechanically damaged or loose fastening of the injection pump.
3. The connections of the return pipeline and the fuel supply pipeline are reversed.
4. There is damage in the fuel supply line:
- Pipelines or hoses are mechanically damaged or clogged, - clean the fuel pipes;
- Fuel filter clogged. Replace filter element.
- In winter, you should check the filter and pipelines for the presence of ice or wax, - drive the car into a heated garage, add gasoline to the system;
- Clogged tank vent or fuel intake strainer - clean.
5. The adjustment of the start of the fuel supply is knocked down.
6. Injectors are faulty, - when the union nut of the fuel line of the faulty injector is loosened, the engine speed will not drop.
7. Faulty high pressure fuel pump (injection pump). Install a new or known-good injection pump for testing.
Cylinder misfiring at idle
1. Worn or dirty spark plugs or incorrect spark plug gap.
2. There is a malfunction of the components of the power system or electrical equipment.
3. Faulty BB wiring.
4. Low-quality fuel is filled, or the fuel filter is blocked.
5. There is a loss of vacuum in the intake manifold or through the hose connections.
6. Insufficient or unevenly distributed compression pressure in the cylinders.
7. There are violations in the operation of the engine management system.
There are gaps in the operation of the engine cylinders when the vehicle is moving in gear
1. Blocked fuel filter or contaminated fuel system.
2. Faulty or dirty spark plugs or incorrect spark plug gap.
3. There is a malfunction of the components of the power system or electrical equipment.
4. There is a defect in the explosive wiring.
5. Components of systems of decrease in toxicity of the fulfilled gases are faulty.
6. Insufficient or unevenly distributed compression pressure between the cylinders.
7. Faulty ignition system.
8. Vacuum loss occurs at the throttle body, intake manifold, or through the vacuum hoses.
The engine spontaneously stalls
1. Idle speed adjustment is broken.
2. The patency of the fuel filter is broken, or moisture or dirt has got into the power system.
3. There is a failure of the components / information sensors of the power system.
4. Components of systems of decrease in toxicity of the fulfilled gases are faulty.
5. Faulty or dirty spark plugs or incorrect spark plug gap (see chapter Ongoing care and maintenance). If equipped, also check the condition of the BB wiring.
6. There are vacuum losses at the throttle body or through the vacuum hoses.
The engine does not develop full power
1. There is a malfunction of the components of the power system or electrical equipment.
2. Air cleaner clogged.
3. Faulty spark plugs or incorrect spark plug gap.
4. Faulty ignition coil.
5. AT fluid level dropped (see chapter Ongoing care and maintenance).
6. Transmission slips.
7. Blocked fuel filter and/or dirt/moisture in the fuel system.
8. Wrong grade of fuel filled. Fill the tank with fuel with the required octane rating.
9. Damaged turbocharger control valve (with appropriate equipment).
10. Faulty timing camshaft activator.
11. Insufficient compression pressure, or its uniform distribution between the cylinders is disturbed.
Optional for diesel engine
1. Air cleaner clogged.
2. Uneven fuel supply of high-pressure fuel pump in cylinders. Adjust on a warm engine.
3. Incorrectly set the moment of the beginning of the fuel injection pump.
4. Clogged fuel filter or injection pump/injector.
5. Adjustment of the maximum frequency of rotation of the crankshaft is violated.
There are pops in the intake system or shots in the exhaust system
1. There is a malfunction of the functioning of the components of the power system or electrical equipment.
2. There is a defect in the secondary circuit of the ignition system (destruction of spark plug insulators or damage to explosive wiring).
3. The fuel injection system needs to be adjusted, or its components are excessively worn.
4. There is vacuum loss at the throttle body, intake piping, or through the vacuum hoses.
5. Stuck valves.
6. The procedure for connecting the explosive wiring is violated.
Detonation sounds occur when accelerating or going uphill
1. Poor quality fuel filled.
2. There is a malfunction of the functioning of the components of the power system or electrical equipment.
3. Wrong type spark plugs installed.
4. Basic ECM settings are violated.
5. Faulty knock sensor.
6. There are vacuum losses.
Engine continues to run after key is turned to position 0
1. Excessively high idle speed.
2. There is a malfunction of the electrical equipment, control components or fuel shut-off valve (diesel models).
3. The functioning of the purge valve of the adsorber of the fuel vapor recovery system is broken (EVAP).
4. Excessive engine operating temperature. Possible causes of this problem could be a low coolant level, a failed thermostat, a blocked radiator, or a faulty water pump.
Excessively smoky diesel engine exhaust
1. Black smoke:
- The air cleaner is dirty, - wash and refill with fresh oil or replace the element;
- Wrong fuel used, - flush the tank and change the fuel;
- Incorrectly set the moment of the beginning of the supply of high pressure fuel pump.
- The injector valve seal is broken. Check the operation of the nozzle on the stand, if necessary, disassemble and grind the valve, or replace the nozzle assembly.
2. Blue smoke:
- Burning oil in the combustion chamber due to wear of the piston rings, the presence of oil in the air cleaner, wear of the seals in the turbocharger covers, the formation of leaks in the gasket between the crankcase and the turbocharger - repair the engine, replace the seals, tighten the turbocharger mounting bolts or replace the gasket;
- Fuel is not supplied to one of the injectors, - check by heating the exhaust pipes of the manifold;
- Poor atomization of fuel by the injector due to a valve malfunction or a break in the atomizer - lap the valve or replace the injector.
3. White or brown smoke:
- Low temperature in the cooling system, - check the thermostat;
- Poor operation of nozzles due to wear or breakage of the atomizer - replace the atomizer.
Engine electrical equipment
Note. Procedures of diagnostics of an electronic control system and codes of malfunctions are given in the Chapter Engine Electrical Systems.
Decreased capacity or insufficient battery charge
1. The alternator drive belt is worn or damaged, or its tension adjustment is broken.
2. Insufficient electrolyte level or severely discharged battery.
3. The battery terminals are corroded or the wire ends are loose.
4. The generator does not provide the required charging current.
5. Broken or otherwise damaged charging circuit wiring, or loose wires at terminals.
6. A short circuit in the electrical wiring creates a permanent leakage of current generated by the battery to «mass».
7. There is an internal defect in the battery.
The charging indicator lamp does not go out when the rpm is increased
1. Loose drive belt.
2. Torque converter overrunning clutch damaged (only turbodiesel). Remove the alternator and turn the alternator drive shaft to the left - if the pulley face does not rotate, then the damage is usually in the overrunning clutch.
3. Damaged voltage regulator/alternator. Disconnect the wire (D+) on the back of the generator and turn on the ignition. Next, check the condition of the generator voltage regulator.
4. Worn brushes.
5. Damaged wire between generator and voltage regulator.
6. Faulty instrument cluster.
The charging indicator lamp does not light up when the key is turned to the «ON»
1. Burnt out or otherwise failed control lamp on the instrument panel.
2. The generator is faulty.
3. There is a defect in the printed circuit board, wiring inside the instrument cluster unit or lamp socket.
The charging indicator lamp does not go out when the key is turned to position 0
1. Broken diodes.
Starter
Attention! The contact terminals of the electrical wiring must be securely fastened and not oxidized!
1. If the starter does not turn, first check that the required voltage is present at terminal No. 50 of the traction relay (minimum 10 V). If the test results are negative, the condition of the electrical wiring of the starter current circuit should be assessed (see Wiring diagrams).
2. To verify that the starter operates properly at full battery voltage, do the following:
- With no gear engaged, turn the key to position «ON»;
- Bridge terminals 30 and 50 of the starter with a wire of at least 4 mm2.
3. If the starter works flawlessly, the cause of the malfunction should be sought in the wires to the starter. If the starter does not work, it should be checked in the removed state.
Starter does not rotate when turned on with the ignition switch
1. Low battery.
2. Jumper terminals 30 and 50 of the starter: if the starter rotates, check the wire 50 connected to the lock for an open, also evaluate the condition of the starter switch.
3. The ground wire is broken, or the quality of its terminal connection is broken, the battery is discharged.
4. The weakening of the current strength due to a violation of the quality or oxidation of the contact connections.
5. There is no voltage at terminal 50 of the traction relay as a result of a broken electrical wiring or damage to the starter switch.
The starter rotates slowly and does not turn the crankshaft
1. Low battery.
2. Filled with summer oil.
3. Insufficient current flow due to loose or oxidized connectors.
4. The carbon brushes are loose on the commutator, stuck in the guides, worn, broken, oily or dirty.
5. Insufficient distance between brushes and commutator.
6. The collector is grooved or burnt and oily.
7. No voltage at terminal 50 (minimum 8 V).
8. Broken bearing.
9. Faulty traction relay.
Starter «grasps», but provides only jerky cranking of the engine
1. Defective gear drive.
2. The gear is dirty.
3. Faulty flywheel ring gear.
Starter gear does not disengage from flywheel/drive plate ring gear
1. Dirty or damaged gear drive components.
2. Faulty traction relay.
3. Return spring is weak or broken.
The starter continues to work after the ignition key is released
1. The traction relay is stuck, - immediately turn off the ignition and replace the traction relay.
2. The ignition lock does not turn off - disconnect the battery, replace the lock.
Supply system
Excessive fuel consumption
All models
1. Air filter element dirty or blocked.
2. Insufficient tire pressure or wrong size tires fitted.
3. The engine has mechanical damage. Check the compression, if necessary, make the appropriate reconditioning.
4. Excessively high idle speed and maximum speed.
Petrol models
1. There is a malfunction of the components of the power system, electrical equipment or electronic control.
2. Leaks in the air intake system.
3. There is damage in the exhaust/catalytic converter system.
diesel engine
1. Clogged fuel return line. Blow out the pipeline with air in the direction from the injection pump to the fuel tank.
2. The tightness of the fuel system is broken. Visually check all piping (supply, return and high pressure), fuel filter and injection pump. Check the system for leaks.
There are fuel leaks and/or a smell of gasoline
1. There are leaks in the fuel lines or vent lines.
2. Fuel tank full. Refuel only until the gun automatically shuts off.
3. There are leaks / evaporation from the lines of power systems and reducing the toxicity of exhaust gases.
Engine won't start
Petrol models
1. When the starter is turned on, the electric fuel pump does not work (no noise from work). Tap the pump body lightly to loosen the stuck part. Check the voltage supply to the pump (check the safety of the protective fuse and the reliability of the fastening of the contact terminals of the corresponding electrical wiring).
2. Faulty fuel pump relay.
3. Stuck injector valves. Check injectors, replace if necessary. Check the voltage supply to the injectors, - disconnect the injector connector, and connect a diode probe lamp to the wire and turn on the starter: the lamp should start flashing.
4. No signal from Hall ignition sensor or coolant temperature sensor. Check the condition of the relevant electrical wiring, poll the memory of the on-board self-diagnosis system.
5. Damaged, clogged or leaking fuel lines, hoses are defective.
6. Clogged fuel filter.
7. Excess air is sucked into the intake tract as a result of leakage.
8. Vacuum lines are damaged, or there is a violation of the tightness of their fit.
9. Damaged pressure regulator - check residual pressure.
10. Damaged throttle position sensor (TPS).
11. No power to the electronic engine control unit (ECM).
12. Presence of ice or wax in the filter or lines of the diesel engine.
13. Clogged fuel tank ventilation, filter in the tank is clogged.
14. The preheat does not work.
15. Damaged diesel engine fuel cut-off valve.
Diesel models
1. Glow plugs not working. Check.
2. Fuel cut off valve does not open. Check the shut-off valve, engine control units and anti-theft alarms.
3. There is a malfunction in the fuel supply system: Check the fuel supply.
- The pipelines are pinched, clogged or leaky, there are defects in the hoses;
- Clogged fuel filter;
- In winter: accumulation of ice or paraffin in the filter or pipelines, - drive the car into a heated garage;
- The fuel tank ventilation is clogged, or the filter in the tank is blocked.
4. There is a shift in fuel injection timing.
5. There is damage to the nozzle (OK), - alternately unscrewing the union nuts, check the proper functioning of the corresponding cylinder.
6. Injection pump is faulty - try installing a new or known good pump.
Cold engine starts badly, works unstably
1. The content of CO does not meet the regulatory requirements - make an appropriate measurement, check the idle speed.
2. Faulty coolant temperature sensor (ECT) or intake air (IAT).
3. Fuel pressure does not match the required value.
4. Excess air is sucked into the intake tract as a result of leakage.
A warm engine does not start well, runs erratically
1. Leaky air intake system. Check intake system. To do this, leave the engine idling and cover the seals and connections on the intake tract with gasoline. If the speed increases for a short time, repair leaks.
2. Damaged fuel pump check valve.
3. Leaks in the fuel system.
4. Increased fuel pressure in the power system.
5. Malfunction of the fuel vapor recovery system.
6. Plugged or kinked fuel return line to tank.
7. Stuck injector valves. Check injectors, replace if necessary. Check the voltage supply to the injectors, - disconnect the injector connector, and connect a diode probe lamp to the wire and turn on the starter: the lamp should start flashing.
8. No signal from Hall ignition sensor or coolant temperature sensor. Check the condition of the relevant electrical wiring, interrogate the on-board self-diagnosis system.
9. Excess air is sucked into the intake tract as a result of leakage.
10. Damaged pressure regulator - check residual pressure.
11. Damaged throttle position sensor.
12. There is no power supply to the electronic engine control unit.
Engine runs intermittently
1. Electrical connections to the fuel pump are interrupted from time to time. Check the condition of the plug connections and connectors of the electrical wires of the fuel pump, air flow meter and fuel pump relay. Check the fuse and contact points on the fuel pump relay. Clean contacts, replace if necessary.
2. Poor fuel quality, vapor lock formation.
3. Fuel supply too low.
4. Defective fuel filter.
5. Faulty fuel pump.
6. Faulty injectors.
7. The lambda probe is faulty, there are violations in the mixture quality control circuit or there is no heating of the lambda probe.
8. Faulty throttle position sensor.
9. Damaged exhaust manifold or exhaust pipe (there are exhaust gas leaks).
10. Malfunction of the evaporative emission system (EVAP).
11. The fastening of the fuel hoses to the injection pump and the fuel filter of the diesel engine has loosened.
12. When connecting, the supply and return pipelines of the injection pump were reversed.
13. Stuck injector valves. Check injectors, replace if necessary. Check the voltage supply to the injectors, - disconnect the injector connector, and connect a diode probe lamp to the wire and turn on the starter: the lamp should start flashing.
14. No signal from Hall ignition sensor or coolant temperature sensor (ECT). Check wiring, poll ECM memory for trouble codes.
15. Excess air is sucked into the intake tract as a result of leakage.
16. Damaged or leaking vacuum lines
17. Damaged pressure regulator - check residual pressure.
18. Damaged throttle position sensor.
19. There is no power supply to the electronic engine control unit.
The engine runs intermittently during transients and at idle
1. Leaky air intake system. Check intake system connections. Start the engine and lubricate the contact points and connections in the intake tract with gasoline. If the engine speed briefly increases, eliminate the cause of the leak.
2. Incorrect idle adjustment. Check idle air control, throttle position sensor, lambda control.
3. Full load sensor defective or incorrectly adjusted. Check Throttle Position Sensor (TPS).
Hot engine won't start
1. Incorrect adjustment of the CO content. Check CO content and idle speed.
2. Too high pressure in the fuel system - check the fuel pressure, if necessary, replace the pressure regulator.
3. Clogged or bent return line between pressure regulator and fuel tank. Clean or replace piping.
4. Faulty engine temperature sensor.
5. The tightness of the power supply system is broken.
6. The tightness of the intake air path is broken.
The diesel engine is unstable at idle and at the time of starting the car from a place
1. The fastening of the fuel hoses to the injection pump and the fuel filter has loosened. Replace the fuel hoses, secure them with clamps, tighten the hollow bolts.
2. The supply and return pipelines at the injection pump were mixed up. Check fuel line connections.
Engine continues to run after key is turned to position 0
1. The tightness of the injectors is broken.
2. On a diesel engine, the fuel cut-off valve does not work.
Lubrication system
The control lamp does not light up when the key is turned to position «ON»
1. Faulty oil pressure sensor. Turn on the ignition, disconnect the wire from the sensor and short it to «mass», - if the lamp lights up, replace the sensor.
2. The sensor is not energized, the contacts are corroded, - check the condition of the corresponding electrical wiring.
3. The control lamp is faulty.
4. Faulty instrument cluster.
The control lamp does not go out after starting the engine
1. Oil is overheated. If the control lamp goes out after the gas is applied, nothing needs to be done.
The control lamp does not go out after applying gas, or lights up while driving
1. The oil level has dropped.
2. There is a short circuit in the wiring of the oil level sensor.
3. Faulty sensor.
Too low oil pressure at all speeds
1. The oil level has dropped.
2. Clogged oil pickup strainer in sump.
3. Worn oil pump.
4. Damaged crankshaft bearings.
Too low oil pressure at low speeds
1. Reducing valve stuck open due to contamination.
Oil pressure too high at engine speeds above 2000 rpm
1. Pressure reducing valve does not open due to contamination.
Cooling system
Overheat
1. The coolant level has dropped.
2. The water pump drive belt is worn or damaged or its tension adjustment is broken.
3. The internal channels of the radiator are blocked or dirty (blocked) radiator grille.
4. Faulty thermostat.
5. Broken or cracked fan blades.
6. Faulty fan switch switch: when the red-yellow and red-white wires of the sensor are shorted, the fan should run at half speed.
7. Faulty coolant temperature gauge.
8. Faulty water pump.
9. The radiator cap does not hold pressure - check the cap under pressure.
Hypothermia
1. Faulty thermostat.
2. The readings of the temperature meter are inaccurate.
External coolant leaks
1. Damaged or destroyed as a result of aging of the material, the hoses or loosened their fastening on the fittings.
2. The seals of the water pump are damaged, - the coolant will ooze through the control hole in the pump housing.
3. There are leaks from the internal channels of the radiator or side reservoir (ov).
4. There are leaks from the engine drain plug or water gallery squeeze plugs.
Internal coolant leaks
Note. Internal coolant leaks are usually identified by checking the condition of the engine oil. Inspect the feeler blade and inside surfaces of the cover (lids) cylinders for traces of water and oil foaming.
1. There are leaks through the cylinder head gasket - perform a pressure test of the cooling system.
2. There are cracks in the cylinder walls or in the head casting.
Loss of coolant occurs
1. Too much coolant has been added to the system.
2. The coolant boils away as a result of engine overheating.
3. There are internal or external coolant leaks.
4. The radiator cap is defective - check the cap with pressure.
Coolant circulation interrupted
1. The water pump is not functioning properly. The easiest way to verify the operation of the pump is to pinch the upper radiator hose while the engine is idling. If a push of liquid is felt inside the hose when the hose is released, the pump is functioning properly.
2. The patency of the cooling system is broken. Drain the coolant (see chapter Ongoing care and maintenance), flush the system and refill it with fresh mixture. If necessary, remove the radiator and backflush it.
3. The water pump drive belt is worn or damaged or its tension adjustment is broken.
4. Stuck thermostat.
Heater
Heater fan not working
1. Fan motor fuse defective.
2. Faulty fan switch - check if voltage is applied to the pre-resistors, remove and check the fan switch.
3. Faulty electric motor. Check if voltage is applied to the fan motor terminals with the ignition on and the fan switch closed, if voltage is applied, replace the motor.
The heater fan does not work on one of the stages
1. Faulty preresistor.
The heater is not switched off by the regulator
1. Faulty switch.
2. Control mixing flap cables are damaged or do not move well.
Heating power too low
1. Insufficient coolant level.
2. The heater control handles are hard to move, defective - check the control assembly, if necessary, replace the corresponding drive cable.
Noise in the heater fan area
1. Dirt, leaves got in, - remove the fan and clean it, clean the air channel.
2. The impeller is out of balance, the bearing is damaged.
Automatic transmission (AT)
Note. Procedures for diagnosing the electronic transmission control system and fault codes are given in the Chapter Engine Electrical Systems.
Due to the complexity of the AT design, it is advisable to diagnose its malfunctions and repair components in a car service workshop or a representative office of Mercedes-Benz.
General problems associated with the functioning of the switching mechanism
1. The number of failures associated with a violation of the adjustment of the shift rod includes the following:
- The engine can be started in transmission positions other than "R" (parking) And "N" (neutral);
- The transmission position indicator reading is different from the actual gear selected;
- The vehicle is moving with the transmission in position "R" or "N";
- Transfers are switched with difficulty or arbitrarily.
2. Adjust the shift rod.
Transmission slips, shifts hard, makes strange noises or does not move the car when set to one of the forward or reverse gears
1. There are many possible causes of the problems listed in the title, but only one of them falls under the competence of an amateur mechanic - the wrong level of transmission fluid.
2. Before driving the car to a car service workshop, check the level and condition of the transmission fluid. Adjust the level as required Specifications or change the fluid along with the filter. If the situation does not improve, seek help from specialists.
Transmission fluid leaks
1. AT liquid has a dark red color. Traces of its leaks should not be confused with traces of impellent oil, which can be carried to the transmission crankcase by the oncoming air flow.
2. To identify and locate the source of the leak, first remove all traces of dirt and grease from the transmission boat. Use a suitable degreaser and/or steam clean. Then drive the car for a short trip at low speed (so that traces of the leak are not carried away by the oncoming flow far from its source). Stop, jack up the vehicle and locate the source of the leak by visual inspection. Most often these are:
- Transmission oil pan, - tighten the fixing bolts and/or replace the oil pan gasket;
- Fluid fill tube, - replace the rubber seal at the point where the tube enters the transmission housing;
- Transmission fluid lines, - tighten union connections or replace lines;
- Ventilation tube - Transmission is overfilled and/or water has entered it.
The oil is brown or smells of burning
1. Insufficient transmission fluid level.
Kickdown mode does not turn on when fully depressing the pedal (no downshift)
1. Dropped ATF level.
2. Faulty engine management system.
3. Faulty sensor-switch or its electrical wiring.
4. Adjustment of a drive cable of the selector is broken.
The engine does not start at any position of the selector or starts in positions other than «R» And «R»
1. The adjustment of the start enable sensor-switch is broken.
2. Serviceability of functioning of a control system of the engine is broken.
3. Adjustment of a cable of the selector is broken.
Transmission slips, jerks or noises when shifting gears. The car does not move when the modes are turned on «D» or «R»
1. Dropped ATF level.
2. Faulty sensor or wiring.
3. Serviceability of functioning of a control system of the engine is broken.
Bridges
Extraneous noise
1. Ordinary road noise - not amenable to adjustment.
2. Tire noise - check the condition of the treads and tire inflation pressure.
3. Worn or damaged wheel bearings or loose torque.
Vibrations
1. Check the condition of the wheel bearings by alternately jacking up the corresponding one from the corners of the car and rotating the wheel manually. Listen for sounds coming from the bearing. Remove the bearings and check their condition.
Oil leaks
1. Damaged differential seals.
Brake system
Note. Before concluding that there is a problem with the braking system, check that the tires are in good condition and inflated to the correct pressure, that the front wheel alignment is not out of alignment, and that the vehicle is not loaded unevenly.
Increased brake pedal travel
1. The working circuit of the brake path is damaged - check the system for leaks.
Brake pedal springs and falls
1. Air got into the brake path - bleed the system.
2. The liquid level in the GTZ tank has dropped, - make the appropriate adjustment, pump the system.
3. The formation of steam bubbles. It appears mainly when the brakes are heavily loaded. Change the brake fluid, remove air from the system.
Decreased braking effect, pedal fails
1. The tightness of the hydraulic path is broken.
2. Cuffs in the main or working brake cylinders are damaged.
Poor braking despite high pedal pressure
1. Oily brake pads.
2. Wrong or hardened pads installed.
3. The brake booster is faulty.
4. Worn brake pads.
Vehicle pulls to one side when braking
1. The tire pressure is not correct.
2. The treads are unevenly worn.
3. Oily brake pads.
4. Different brake pads are installed on the same axle.
5. Excessively worn brake pads.
6. Contaminated caliper shafts.
7. Calipers damaged by corrosion - replace.
8. Unevenly worn pads.
Spontaneous braking
1. The compensation hole in the main brake cylinder is clogged.
2. There is not enough clearance between the drive rod and the GTZ piston.
Brakes get hot while driving
1. The compensation hole in the main brake cylinder is clogged.
2. There is not enough clearance between the drive rod and the GTZ piston.
The brakes are shaking
1. Wrong pads installed.
2. The brake disc is corroded in places.
3. Excessive brake disc runout.
Brake pads do not move away from the brake disc, the wheel is difficult to turn by hand
1. Corrosion in the brake caliper cylinders. Repair the caliper, possibly replace it.
Uneven pad wear
1. Wrong pads installed. Replace pads, install original Mercedes-Benz pads.
2. Calipers damaged by corrosion - replace.
3. The piston stroke is difficult.
4. The tightness of the path of the brake system is broken.
Wedge-shaped brake pad wear
1. The brake disc does not rotate parallel to the caliper.
2. Calipers damaged by corrosion - replace.
3. The piston is out of order.
Screeching brakes
1. Often the cause is atmospheric influence (air humidity). If a creak appears after a long stay in high humidity and then disappears, nothing needs to be done.
2. Wrong pads installed.
3. The brake disc does not rotate parallel to the caliper.
4. The caliper shaft is dirty.
5. The springs for fastening the pads are bent.
6. Compression springs stretched.
Pulsation of the brake pedal
1. A sign of normal operation of ABS.
2. Excessive brake disc runout.
3. The brake disc does not rotate parallel to the caliper.
The ABS warning light comes on while driving
1. Insufficient supply voltage (below 10 V). Check voltage. Check if the generator control lamp goes out after starting the engine. If everything is in order, check the alternator drive V-belt.
2. Has an ABS malfunction, - check the condition and reliability of the fixing of the return pump ground terminal connection (in hydromodulator).
Suspension and steering
Vehicle pulls to one side when moving
1. Tires are unevenly inflated.
2. There is a tire defect.
3. Excessively worn suspension or steering components.
4. Front wheel alignment required.
5. Front brakes seized.
There are jerks, jerks or vibrations
1. The wheels are out of balance or the discs are oval.
2. Worn wheel bearings, loose torque or out of adjustment.
3. Worn or damaged shock absorbers or other suspension components.
There is excessive rocking of the vehicle/» burying» his nose when cornering or braking
1. Defective shock absorbers.
2. Damaged suspension components.
Steering wheel too tight
1. The fluid level in the reservoir of the power steering system has dropped excessively.
2. Tires not properly inflated.
3. Insufficiently lubricated steering gear joints.
4. The adjustment of the angles of installation of the front wheels is broken.
5. The hydraulic booster does not develop the required power.
There is excessive steering play
1. Loose front wheel bearing tightening force.
2. Excessively worn suspension or steering components.
The power steering system does not develop the proper force
1. The power steering pump drive belt is worn or damaged or its tension adjustment is broken.
2. The fluid level has dropped too much.
3. The patency of the hoses or lines of the hydraulic system is broken.
4. Air got into the hydraulic system - bleed the system.
Excessive tread wear (not in one area)
1. Tires not properly inflated.
2. The wheels are out of balance.
3. Damaged wheel rims.
4. Excessively worn suspension or steering components.
Excessive tread wear on outer edge
1. Tires not properly inflated.
2. Too sharp turns are made.
3. The adjustment of the angles of installation of the front wheels is broken (excessive convergence).
4. Bent or twisted suspension arm.
Excessive tread wear on the inside edge
1. Tires not properly inflated.
2. The adjustment of the angles of installation of the front wheels is broken (divergence).
3. Steering components damaged or loose.
There is localized tread wear
1. The wheels are out of balance.
2. Damaged or bent discs.
3. There is a tire defect.
Wiper blade defects
Slippage
1. Rubber working elements are dirty.
2. The edges of the brushes are frayed, the rubber working elements are worn or torn.
In the cleaning field, the remaining water immediately collects in drops
1. The windshield is dirty with varnish or oil.
The brush cleans one-sidedly - one side is good, the other is not
1. The rubber working element has one-sided wear.
2. The wiper arm is twisted, the blade does not fit exactly on the glass.
Uncleaned surfaces
1. The reliability of fixing the working element in the brush frame is broken.
2. The brush does not adhere to the glass evenly.
3. Lever clamping force is too low - Lightly lubricate wiper arm pivots and springs or install a new arm.
Tire defects
Heavy tire wear on both sides of the running surface
1. Tire pressure too low.
Strong tire wear in the middle of the working surface around the entire circumference of the tread
1. Tire pressure too high.
Uneven tread wear
1. Static and dynamic imbalance of the wheel, possibly due to excessive lateral runout of the disc, too much play in the bearing joints.
Uneven wear in the middle of the tread
1. Static wheel imbalance, possibly due to excessive vertical runout.
Strong wear of individual sections in the middle of the tread working surface
1. The result of hard braking.
Sawtooth tread wear, often along with an invisible tear in the tire's fabric base
1. Car overload. Check the condition of the inner walls of the tires.
Rubber tabs on the side edges of the tread (scaly wear)
1. The adjustment of the wheel alignment angles is broken.
2. Tires worn out.
3. Faulty dampers/torsion springs/strut assemblies.
Burr formation on one side of the front wheel tread
1. Adjustment of a convergence of wheels is broken.
2. Tires worn out.
3. Frequent movement on wavy surfaces. Fast cornering.
Cord breaks. At first visible only from the inside
1. Driving over sharp rocks, tire bumps, etc. at high speed.
One-sided wear of the working surface of the tread
1. Check camber adjustment.
2. Has an ABS malfunction, - check the condition and reliability of the fixing of the return pump ground terminal connection (in hydromodulator).