Engine Controls - Tests W/o Codes: Other Mercedes-Benz C-class W202

ENGINE WILL NOT START

Ensure steps for spark and fuel testing in BASIC TESTING article have been performed. Test the following

1. Idle speed air valve.
2. Differential pressure regulator (if equipped).
3. Power and ground circuits.

DIFFICULT COLD START

Test the following

1. Coolant temperature sensor.
2. TDC sensor.
3. Injectors.
4. Idle control system components.

ROUGH IDLE WHEN WARM

Test the following

1. MAP sensor.
2. Oxygen sensor.
3. Crank angle sensor signal (TD signal).
4. Throttle position sensor.
5. Intake air temperature sensor.
6. Fuel injectors.
7. Atmospheric pressure sensor.
8. EGR and other emission components.

IDLE RPM HIGH WHEN WARM

Test the following

1. Electronic accelerator actuator.
2. Cruise control/idle speed control actuator.
3. MAP sensor.
4. Atmospheric pressure sensor.
5. Air intake system.
6. Emission systems.

IDLE RPM LOW WHEN WARM

Test the following

1. Electronic accelerator actuator.
2. Cruise control/idle speed control actuator.
3. Air intake system.
4. MAP sensor.

STALLING DURING WARM-UP

Test the following

1. Air intake system.
2. MAP sensor.
3. Crank angle sensor signal (TD signal).
4. Coolant temperature sensor.
5. Throttle position sensor and other idle controls.
6. Fuel supply.
7. EGR control system.

STALLING AFTER WARM-UP

Test the following

1. EGR control system.
2. MAP sensor.
3. Throttle position sensor.
4. Crank angle sensor signal (TD signal).
5. Vehicle speed sensor.
6. Air intake system.
7. Fuel supply system.
8. Electronic accelerator actuator.
9. Cruise control/idle speed control actuator.

LACK OF POWER

Test the following

1. Brakes binding.
2. Fuel supply.
3. Emission controls.
4. MAP sensor.
5. Crank angle sensor signal (TD signal).
6. Coolant temperature sensor.
7. Atmospheric pressure sensor.
8. Vehicle speed sensor.
9. EZL/AKR ignition control unit (LH-SFI only).
10. Knock sensors.
11. Fuel injectors.
12. Air intake system.
13. EGR control system.

Intermittent Simulation

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly tap on or vibrate suspect component.
2. Heat suspect component.
3. Wiggle or bend wiring harness.
4. Spray suspect component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.