Engine Speed (RPM) Sensor G28 , Checking

Engine Speed (RPM) Sensor G28, Checking

NOTE: 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 Motronic Engine Control Module (ECM) J623 fuses 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.

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.
- Switch the ignition on.

- Using the scan tool, check the engine speed:

Diagnostic text Specified value
Engine rotations per minute (RPM) Idle speed

- End diagnosis and switch ignition off.

If the specified value was not obtained:

Procedure
- Raise the vehicle.







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

Checking internal resistance







- Using a multimeter, check the Engine Speed (RPM) Sensor G28 terminals 2 to 3 - B - for resistance.
Specified value: 730 to 1000 Ohms (at approx. 20 degrees C)
- Using a multimeter, check the Engine Speed (RPM) Sensor G28 terminals 1 to 2 and 1 to 3 for short circuits.
Specified value: Infinity (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.

If the manufacturers test box is not being used. Perform the following step.
- Remove the Motronic Engine Control Module (ECM) J623.
- Using a Multimeter, check the Engine Speed (RPM) Sensor G28 electrical harness connector terminals to the Motronic Engine Control Module (ECM) J623 electrical harness connector T60 terminals for an open circuit.

Engine Speed (RPM) Motronic Engine Control Module
Sensor G28 electrical harness (ECM) J623 electrical connector
connector terminals T60 terminals or test box sockets
1 26
2 36
3 51

Specified value: 1.5 Ohms Max.

If the specification was not obtained:
- Check the wiring for a short circuit to each other, Battery (+), Ground (GND), or an open circuit.
- Check the electrical harness connector for damage, corrosion, lose 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 Motronic Engine Control Module (ECM) J623.

Final procedures
After repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If the DTC memory was erased, generate readiness code.

- End of diagnosis.