Engine Speed Sensor, Checking

Engine Speed Sensor, Checking

Special tools, testers and auxiliary items required

• Multimeter

• wiring diagrams

• Use only gold-plated terminals when servicing terminals in harness connector of Engine Speed (RPM) Sensor (G28).

Test requirements

• Fuses for Engine Control Module (ECM) (J623) OK.

• Battery voltage at least 12.5 volts.

• All electrical consumers such as, lights and rear window defroster, switched off.

• Vehicles with automatic transmission, shift selector lever into position " P" or "N".

• A/C switched off.

• Ground (GND) connections between engine/transmission/chassis OK.

• Ignition switched off.

• Test procedure

• Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check.

• Start diagnosis

Function

The Engine Speed (RPM) Sensor (G28) detects RPM and reference marks. Without an engine speed signal, the engine will not start. If the engine speed signal fails while the engine is running, the engine will stop immediately.

Function test

- Connect the scan tool.

- Start engine and let it run at idle.

- Select "Diagnostic mode 1: Check measured values".

- Select the measuring value "PID 12: Engine rotations per minute (RPM)".

- Check specified value:





If specified value is not obtained:

- End diagnosis and switch ignition off.

- Check resistance of Engine Speed (RPM) Sensor ( G28) and wires:

Test sequence

- Disconnect the electrical harness connector - 3 - from the Engine Speed (RPM) Sensor (G28).





- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

- Using a multimeter , check Engine Speed (RPM) Sensor (G28) component terminals 2+3 for resistance.





Specified value: 0.7 to 1000 kOhm

If specification is not obtained:





- Replace Engine Speed (RPM) Sensor (G28).

If the specified value is obtained:

- Using a multimeter , check Engine Speed (RPM) Sensor (G28) for short circuit between terminals 1 + 2 as well as 1 + 3.

Specified value: infinite ohms

If the specification is not obtained:

- If necessary, repair the wiring connection.

If the specified value is obtained:

- Using a Multimeter, check the following wiring connection for an open circuit.









Specified resistance 1.5 ohms max.

If the specification is not obtained:

- Check the wiring for a short circuit to Battery positive (+) or an open circuit.

- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:

Wires OK:

- Remove Engine Speed (RPM) Sensor (G28) and check sensor wheel for proper seating, damage and run-out.

If the sensor wheel is OK:

- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

- Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to => [ Readiness Code ] Readiness Code.

- End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

- Replace the Engine Control Module (ECM) (J623 ) => [ Motronic Engine Control Module, Replacing ] Motronic Engine Control Module, Replacing.

- Assembly is performed in the reverse of the removal.

Final procedures

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code, Setting ] Readiness Code, Setting.

End of Diagnosis.