Engine Speed Sensor: Testing and Inspection

Engine Speed Sensor, Checking

The Engine Speed (RPM) Sensor (G28) provides the engine speed signal. If the Engine Speed (RPM) Sensor (G28) fails, the engine continues to run using a back up signal from the Needle Lift Sensor (G80).

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

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) fuses OK.

• Battery voltage at least 12.5 volts.

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

• A/C switched off.

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

• Ignition switched off.

Function

The Engine Speed (RPM) Sensor (G28) detects RPM and reference marks. Without an engine speed signal, the engine will not start.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ General Diagnosis ] General Diagnosis.

Start diagnosis

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

Checking internal resistance

- Using a multimeter, check the Engine Speed (RPM) Sensor (G28) terminals 1 to 2 for resistance.





Specified value: 0.7 to 1000k ohms.

- Check Engine Speed (RPM) Sensor (G28) terminals 1 to 3 and 2 to 3 for short circuits.

Specified value: infinite (infinity)

If any of the specified values are not obtained:

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

If the specified values are obtained:

Checking wiring

If the manufacturers test box is being used, perform the following step.

- Install the test box. Refer to => [ 68-Pin Test Box Adapter, VAG1598/19, Installing ] Diesel Direct Fuel Injection ECM, Checking.

If the manufacturers test box is not being used, perform the following step.

- Remove the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248). Refer to => [ Diesel Direct Fuel Injection ECM, Replacing ] Diesel Direct Fuel Injection ECM, Checking.

- Using a Multimeter, check the Engine Speed (RPM) Sensor (G28) electrical harness connector terminals to the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) electrical harness connector T60 terminals for an open circuit.









Specified value: 1.5 ohms Max.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

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

- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring:

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

If the sensor wheel is OK:

- Replace the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248). Refer to => [ Diesel Direct Fuel Injection ECM, Replacing ] Diesel Direct Fuel Injection ECM, Checking.

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 ] Monitors, Trips, Drive Cycles and Readiness Codes.