Troubleshooting — Engine (Audi A4 B7)

Basic checks for difficult engine starting

Petrol models

Assess the external condition of all electrical wiring in the engine compartment, make sure there are no signs of damage to the insulation, oxidation or loosening of the contact connections. Check for blown fuses in the mounting block and whether the battery is in good condition. Next, make sure that the vacuum hoses are routed correctly, in good condition and securely fastened. Don't forget to also check the intake air tract components for signs of developing leaks.

If no obvious violations can be identified during a visual inspection, the compression pressure in the engine cylinders should be checked (see Section 2 Chapter 2).

Another important mechanical check is to check the patency of the engine exhaust tract. The check is performed using a pressure gauge or a vacuum gauge. In the first case, unscrew the lambda probe or the control valve of the air mixing system into the exhaust gases (depending on the configuration). Screw a pressure gauge with a measurement range of 0÷0.35 kgf/cm² into place of the removed component and start the engine at 2500 rpm. If the back pressure in the exhaust tract is more than 0.14 kgf/cm², there is a violation of its patency (most likely, the catalytic converter is not working properly). When using a vacuum gauge, connect it to the vacuum fitting of the intake manifold, start the engine and read the meter reading. Partially open and fix the throttle valve - a slow drop in the depth of vacuum after the speed stabilizes will also indicate a violation of the patency of the exhaust tract.

Checking the fuel supply

Note: Before performing most of the following checks, the fuel system must be depressurized (see Chapter 4).

At this stage of the basic diagnostics, perform the following checks (see Chapter 4):

• checking the regulated fuel pressure;
• checking the tightness of fuel system components;
• checking the fuel pump relay;
• assessment of the condition of fuel injectors.

Checking the proper functioning of the ignition system

First of all, you should make sure that the spark plugs are working properly - it is best to check them with a special tester. If any faults are detected, measure the specific resistance of the high-voltage wiring - the measurement result should not exceed 16 kOhm/m.

Next, you should check the serviceability of the power supply to the module or ignition coils and measure the resistance of the primary and secondary circuits of the module or ignition coils.

Diesel models

The conditions that must be met to ensure the successful start of any diesel engine include:

• sufficient engine crankshaft speed to start;
• sufficient temperature of compressed air in the combustion chamber for spontaneous combustion of the fuel, i.e. achievement of the specified compression pressure and, when starting in cold weather, proper functioning of the glow plugs;
• fine spraying (injection) of fuel into the combustion chambers at exactly the right moment.

First of all, you should make sure that the starter is working properly, then check the fuel supply, injectors and the operation of the pre-heating system.

1. The engine does not turn over when trying to start it

1. There is corrosion of the battery terminals, or the fastening of the wire tips to them has become loose.

2. The battery is discharged or faulty: if there are no violations under the previous point, with the ignition on, turn on the headlights and/or windshield wipers - failure of the electrical devices to function properly confirms the fact that the battery charge level has dropped excessively.

3. The wiring in the engine starting system circuit is broken or the wires are loose at the terminals.

4. The starter gear is jammed in the toothed ring of the drive disk.

5. The starter traction relay is faulty.

6. The starter is faulty.

7. The ignition switch is faulty.

2. The engine turns over but does not start

1. The start is not performed correctly (see chapter "Controls and operating techniques").

2. The engine immobilizer is faulty or not disabled.

3. The compression value is insufficient.

4. The engine oil is too thick.

Petrol models

5. The fuse for the electric fuel pump or electronic injection system is faulty.

6. The fuel tank is empty or filled with low-quality fuel.

7. The air filter is heavily contaminated.

8. As a result of a leak in the air intake tract, air is sucked in and there is a loss of vacuum in the vacuum tract.

9. There are losses of vacuum in the air supply elements, malfunctions in the fuel injection and ignition control systems.

10. The battery is discharged (insufficient engine cranking speed).

11. The battery terminal connections are oxidized or have become loose.



12. The fuel pump is faulty, or its relay is damaged - check by ear that the pump is activated properly when the ignition is turned on.

13. Ignition system components are damaged or excessively damp.

14. Spark plugs are worn or faulty, or the spark plug gap is set incorrectly.

15. The starting system wiring is broken or disconnected, or the wires are loose at the terminals.

16. The wiring of the ignition coil (module) is broken or disconnected, or the wires on the terminals of the coil (modules) are loose.

17. The engine control unit fuse is damaged, the engine control system sensors are faulty.

Diesel models

Note: Make sure that when the pre-heating system is operating, (when the preheater K/L is on) all on-board electrical consumers (light, heated rear window, audio system, etc.) were disabled.

18. Pre-electric fuel pump fuse blown (if available) or preheating systems.

19. The engine is not warmed up: check the proper functioning of the pre-heating system.

20. There is no voltage on the fuel shut-off solenoid valve, or the solenoid valve is faulty.

21. There is damage to the fuel supply lines, or air has entered them.

22. The patency of the return fuel tract is impaired.

23. The fuel filter is clogged.

24. The adjustment of the moment of start of fuel supply is knocked down.

25. The injectors are faulty - when the union nut of the fuel line of the faulty injector is loosened, the engine speed will not drop.

26. The high-pressure fuel pump (HPFP) is faulty.

3. The starter operates without turning the engine

1. The starter gear is jammed.



2. The teeth of the starter gear or flywheel ring gear are worn or damaged.

4. Difficulty starting a cold engine. Also refer to Section 30.

1. The battery is discharged or its charge level is insufficient.

2. The functioning of the power supply system components or electrical equipment is disrupted.

3. Paraffin deposits in the fine fuel filter (diesel models), - warm up or replace the filter element and fill the car with winter diesel fuel, or add low-octane gasoline to the tank in a ratio of 1/3.

4. The glow plugs of the diesel engine are faulty.

5. Difficulty starting a hot engine. Also refer to Section 31.

1. The air filter is clogged.

2. The functioning of the power supply system components or electrical equipment is disrupted.

3. Fuel does not reach the injectors/nozzles of the injection system.

4. The fuel injection advance angle of the diesel engine is out of order.

5. The diesel engine high pressure fuel pump is faulty or its adjustment is incorrect.

6. Insufficient compression pressure.

6. The starter engages too noisily or with difficulty

1. The teeth of the starter gear or flywheel ring gear are worn or damaged.

2. The starter mounting fastener is lost or the tightening force has weakened.

7. The engine starts but immediately stalls

1. The engine immobilizer is faulty.

2. The electrical wiring is faulty, or the wires on the terminals of the ignition coil or generator are loose.

3. There is a malfunction of the power supply system components or electrical equipment.

4. The basic settings of the engine control module (ECM) are violated.



5. There is damage in the exhaust system/catalytic converter.

6. There are losses of vacuum at the throttle body, intake manifold or through vacuum hoses.

7. Insufficient compression pressure.

8. Idle speed adjustment is incorrect.

9. The patency of the return fuel tract of the diesel engine is impaired.

10. The glow plugs of the diesel engine are switched off too early.

11. The fuel injection advance angle of the diesel engine is out of order.

12. The fuel injection pump is faulty.

13. The diesel engine fuel shut-off solenoid valve is jammed.

8. The stability of the engine operation at idle speed is impaired

Note: If the engine speed is unstable (for example, when misfiring) to avoid damage to the catalytic converter, try to run the engine only for short periods of time and do not subject it to excessive loads.

Petrol models

1. There is a loss of vacuum. Make sure that the fasteners are tightened securely, check the fact and quality of fastening on their nipples on the intake manifold of all vacuum hoses. Listen to the running engine using a stethoscope or a section of fuel hose. The presence of a hissing sound will allow you to identify the source of the vacuum "leak" - a solution of soapy water can be used to check no less effectively.

2. The tightness of the intake manifold fit on the cylinder head is broken.

3. The cylinder head gasket is broken - measure the compression pressure in the engine cylinders (see Chapter 2).

4. Timing drive components are worn out.

5. The working projections of the camshaft cams are worn out.



6. The engine is overheated.

7. The PCV system valve is clogged.

8. There are leaks through the EGR valve.

9. There is a malfunction of the power supply system components or electrical equipment.

10. The air filter is clogged.

11. The fuel pump does not supply sufficient fuel to the injectors.

Diesel models

12. The quality of the connections of the fuel hoses on the high-pressure fuel pump and fuel filter is damaged.

13. The fuel injection pump mount has become loose.

14. The connections of the return line and the fuel supply line are reversed.

15. There is damage in the fuel supply lines.

16. The patency of the return fuel tract is impaired.

17. The slow idle speed adjustment is out of order.

18. Air has entered the fuel system.

19. The fuel injection start adjustment is out of adjustment.

20. The injectors are faulty - when the union nut of the fuel line of the faulty injector is loosened, the engine speed will not drop.

21. The fuel injection pump is faulty. Install a new fuel injection pump or a known good one for testing.

9. There are misfires in the cylinders at idle speed

Note: If the engine speed is unstable (for example, when misfiring) to avoid damage to the catalytic converter, try to run the engine only for short periods of time and do not subject it to excessive loads.

1. Spark plugs are worn or dirty, or the spark plug gap is set incorrectly.

2. There is a malfunction of the power supply system components or electrical equipment.

3. The high-voltage wiring is faulty (with appropriate equipment).



4. Poor quality fuel has been added or the fuel filter is clogged.

5. There are losses of vacuum in the intake manifold or through hose connections.

6. Insufficient or unevenly distributed compression pressure in the cylinders.

7. There are malfunctions in the engine control system.

10. There are misfires in the engine cylinders at speeds above idle/when the vehicle is moving in gear

Note: If the engine speed is unstable (for example, when misfiring) to avoid damage to the catalytic converter, try to run the engine only for short periods of time and do not subject it to excessive loads.

1. The fuel filter is clogged or the fuel line is blocked.

2. The spark plugs are faulty or dirty, or the spark plug gap is set incorrectly (gasoline engines).

3. Components of the power supply system or electrical equipment are faulty.

4. There is a defect in the high-voltage electrical wiring (with appropriate equipment).

5. Components of exhaust gas toxicity reduction systems are faulty.

6. Insufficient or uneven distribution of compression pressure between cylinders.

7. The ignition system is faulty.

8. There are vacuum losses at the throttle body, intake manifold or through vacuum hoses.

9. The valve mechanism is worn out.

10. Timing phase adjustment is disrupted.

11. The patency of the intake manifold is impaired.

12. The adjustment of the start of fuel supply of the diesel engine is out of order.

13. The car is filled with poor quality diesel fuel.

11. The engine stalls spontaneously

1. Idle speed adjustment is incorrect.

2. The fuel filter is clogged, or moisture or dirt has entered the fuel system.

3. There is a failure of components/information sensors of the engine management system.

4. Components of exhaust gas toxicity reduction systems are faulty.

5. The spark plugs are faulty or dirty, or the spark plug gap is set incorrectly (see Chapter 1). If equipped, also check the condition of the high-voltage electrical wiring.

6. There are losses of vacuum at the throttle body or through the vacuum hoses.

12. The engine does not develop full power

1. There is a malfunction of the power supply system components or electrical equipment.

2. The air cleaner is clogged or the air intake tract is otherwise obstructed.

3. The spark plugs are faulty or the spark plug gap is set incorrectly (gasoline engines).

4. The ignition coil or module is faulty (gasoline engines).

5. The fuel filter is blocked and/or dirt/moisture has entered the fuel system.

6. The wrong type of fuel was filled in.

7. The turbocharger control valve is damaged (with appropriate equipment).

8. Insufficient compression pressure, or its uniform distribution between the cylinders is disrupted.

9. The valves are jammed or the valve springs are weak.

10. The cylinder head gasket is broken.

11. The clutch slips.

12. The engine is overheated.

13. There are losses of vacuum.

14. The working projections of the camshaft cams are worn out.

15. The valve timing is incorrect.

16. There are leaks in the fuel pump.

17. The exhaust system is blocked.

Additional for diesel engine

19. EGR valve is faulty.

20. The maximum crankshaft speed adjustment is not correct.

21. The fuel filter, high-pressure fuel pump or injectors are clogged.

22. The fuel line between the high-pressure fuel pump and the fuel tank is blocked.

23. The patency of the return fuel line is impaired.

24. The uniformity of fuel supply to the cylinders is disrupted.

25. The moment of start of fuel supply by the high-pressure fuel pump is set incorrectly.

13. There are pops in the intake system or shots in the exhaust system

1. The functioning of the components of the power supply system or electrical equipment is disrupted.

2. There is a defect in the secondary circuit of the ignition system of the gasoline engine (destruction of spark plug insulators or damage to high-voltage electrical wiring).

3. The fuel injection system needs adjustment, or its components are excessively worn.

4. There are vacuum losses at the throttle body, intake manifold or through vacuum hoses.

5. The valves are stuck.

6. The ignition timing angle setting is incorrect, for example, as a result of incorrect connection of the high-voltage wiring (with appropriate equipment).

7. EGR valve is faulty.

8. A lean air-fuel mixture enters the cylinders.

14. When accelerating or driving uphill, detonation sounds occur

1. Low-quality fuel was used.

2. The functioning of the components of the power supply system or electrical equipment is disrupted.

3. The wrong type of spark plugs are installed (gasoline engines).

4. The basic ECM settings are violated.

5. The knock sensor is faulty.

6. There are losses of vacuum.

15. The engine continues to run after the ignition is turned off

1. Idle speed is too high.

2. There is a malfunction in the electrical equipment, control components or fuel shut-off valve (diesel models).

3.The electric purge valve of the fuel vapor capture system (EVAP) is not functioning properly.

4. Excessively high engine operating temperature (low coolant level, thermostat failure, blocked radiator or water pump failure).

16. Excessive smoke from the diesel engine exhaust

1. Black smoke:

• the air cleaner is dirty - wash or replace the filter element;
• the wrong fuel was filled in - flush the tank and change the fuel;
• the injection pump start time is set incorrectly, or the pump itself is faulty;
• the injector valve is not tight enough. Check the injectors on the bench, if necessary, disassemble and grind the valve, or replace the injector assembly;
• eGR valve is faulty.

2. Blue smoke:

• oil gets into the combustion chamber due to wear of piston rings, its presence in the air cleaner, wear of seals in turbocharger covers, formation of leaks in the gasket between the crankcase and turbocharger - repair the engine, replace the seals, tighten the turbocharger mounting bolts or replace the gasket;
• the fuel supply to one of the injectors is disrupted - check by heating the exhaust pipes of the manifold;
• the quality of fuel atomization by the injector is impaired due to a faulty valve or a broken atomizer - grind the valve or replace the injector.

3. White or brown smoke:

• coolant temperature is insufficient - check thermostat;
• the injectors are not functioning properly due to wear or breakage of the atomizer - replace the atomizer.