Engine Controls - Trouble Shooting - No Codes: Other Audi A4 B5 facelift

WILL NOT START (CRANKS OKAY)

Spark Available

1. Check fuel system fuse and fuel pump relay.
2. Verify air intake system is unrestricted.
3. Ensure fuel system pressure and volume are correct.
4. Check for poor quality or contaminated fuel.
5. Check for condensation (water) in fuel tank, causing fuel pump to freeze (cold climate).
6. Check exhaust system for restriction.

No Spark Available

1. Ensure secondary ignition system is in good condition.
2. Ensure ignition coil supply voltage is correct.
3. Ensure ignition coil primary resistance is correct.
4. Ensure ignition coil secondary resistance is correct.
5. Check camshaft position sensor operation.
6. Ensure PCM has correct voltage supply and is properly grounded.
7. Check vehicle for aftermarket electronic equipment that may have been installed incorrectly.

DIFFICULT START (CRANKS OKAY)

1. Ensure sufficient secondary spark is available.
2. Check air induction system for cracks and restriction.
3. Ensure vacuum hoses are not disconnected or damaged.
4. Ensure fuel system pressure and volume are correct.
5. Ensure fuel system residual pressure is correct.
6. Ensure fuel injector operation is correct.
7. Ensure EGR valve operation is correct (2.8L).
8. Check for cracks and poor connections at throttle body.
9. Ensure ignition and valve timing are correct.
10. Check ignition coil primary connections and wiring harness.
11. Ensure ignition coil resistance is within specification.
12. Check Engine Coolant Temperature (ECT) sensor operation.
13. Ensure electrical harness and connectors are not broken or loose.
14. Ensure PCM has correct voltage supply and is properly grounded.
15. Ensure engine has sufficient compression.

ENGINE SURGES

1. Ensure no vacuum leaks exist.
2. Ensure EGR valve operation is correct (2.8L).
3. Check Throttle Position (TP) sensor operation.
4. Check throttle shaft for excessive wear.
5. Ensure fuel system pressure is correct and consistent.
6. Ensure ignition timing is correct.

ROUGH OR UNSTABLE IDLE

1. Check air intake system for restrictions.
2. Ensure fuel system pressure and volume are correct.
3. Check fuel injector electrical connections.
4. Use stethoscope to verify consistent operational noise coming from fuel injectors.
5. Ensure fuel injector spray pattern is correct.
6. Ensure sufficient secondary spark is available in all cylinders.
7. Ensure vacuum hose routing is correct and no vacuum leaks exist.
8. Check throttle position sensor operation.
9. Check for EGR system malfunction (2.8L).
10. Check Engine Coolant Temperature (ECT) sensor operation.
11. Check Heated Oxygen Sensor (HO2S) voltage output.
12. Check for poor quality fuel.

Note. Prolonged use of poor quality fuel can cause injector clogging and carbon build-up on intake system.

EXCESSIVE FAST IDLE

1. Check throttle cable adjustment.
2. Ensure vacuum hose routing is correct.
3. Ensure no vacuum leaks exist.
4. Ensure fuel system pressure and volume are correct.
5. Check Engine Coolant Temperature (ECT) sensor operation.

ENGINE STALLS

1. Ensure air intake system is unrestricted.
2. Ensure PCV system operation is correct.
3. Check EGR system for correct operation (2.8L).
4. Check Idle Air Control (IAC) valve.
5. Check for cracks and poor connections at throttle body.
6. Check Throttle Position (TP) sensor operation.
7. Check Engine Coolant Temperature (ECT) sensor operation.
8. Ensure fuel system pressure is correct.
9. Check for poor quality fuel, fuel with high alcohol content or contaminated fuel.

ENGINE LACKS POWER

1. Ensure throttle valve opens completely when accelerator pedal is fully depressed.
2. Ensure air intake system is unrestricted.
3. Check deceleration fuel shut-off valve operation (1.8L turbo).
4. Check Mass Airflow (MAF) sensor.
5. Check intake manifold change-over valve.
6. Ensure fuel system pressure and volume are correct.
7. Ensure base timing is correct and timing advance system is functional.
8. Check Engine Coolant Temperature (ECT) sensor operation.
9. Check transmission for correct downshift (A/T).
10. Check fuel tank filler tube for tampering of restrictor. If tampering has occurred, check catalytic converter for lead contamination and exhaust system restriction.
11. Check for poor quality fuel containing insufficient cleaning additives.

Note. Prolonged use of poor quality fuel can cause injector clogging and carbon build-up on intake system.

ENGINE MISFIRES OR HESITATES

1. Ensure vacuum hoses are not disconnected or damaged.
2. Ensure electrical harness connectors and wires are not broken or loose.
3. Ensure fuel pressure is correct.
4. Check Throttle Position (TP) sensor operation.
5. Check Mass Airflow (MAF) sensor.
6. Check Engine Coolant Temperature (ECT) sensor operation.
7. Check Heated Oxygen Sensor (HO2S) voltage output.

AFTERBURN IN EXHAUST SYSTEM

1. Ensure no leaks exist in exhaust system.
2. Ensure base timing system functions correctly.
3. Check fuel injectors for leaking.
4. Check Engine Coolant Temperature (ECT) sensor operation.

POOR FUEL MILEAGE

1. Ensure base timing and timing advance system is functional.
2. Ensure fuel system pressure is correct.
3. Check air induction system for leaks.
4. Check fuel injector operation.
5. Check Mass Airflow (MAF) sensor.
6. Check Engine Coolant Temperature (ECT) sensor operation.
7. Check Heated Oxygen Sensor (HO2S) voltage output.

DETONATION OR KNOCKING

1. Check engine oil level.
2. Check engine for overheating.
3. Ensure base timing is correct.
4. Check for vacuum leaks.
5. Check EGR system operation (2.8L).
6. Check for contaminated or poor quality fuel.
7. Check for carbon build-up in combustion chamber.
8. Ensure spark plug application is correct.
9. Check for correct torque of knock sensor.
10. Check for correct knock sensor signal.
11. Ensure PCM application is correct.

Intermittent Simulation

To reproduce conditions creating an intermittent fault, use following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source. Monitor circuit/component voltage or resistance while simulating intermittent fault. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.