Engine Speed Sensor: Testing and Inspection

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 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







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

Checking internal resistance







- Using a multimeter , check the Engine Speed (RPM) Sensor G28 terminals 1 to 2 - B - for resistance.
Specified value: 450 to 1000 Ohms (at approx. 20 degrees C).

If the specified value was not obtained:
- Replace the Engine Speed (RPM) Sensor G28.

If the specified value is 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 Engine Control Module (ECM) J623.







- Using a Multimeter , check the Engine Speed (RPM) Sensor G28 electrical harness connector terminals to the Engine Control Module (ECM) J623 electrical harness connector T60 terminals for an open circuit.

Engine Speed (RPM) Sensor Engine Control Module (ECM)
G28 electrical harness J623 electrical connector T60
connector terminals terminals or test box socket
1 53
2 38

Specified value: Wire resistance max 1.5 Ohms.

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 detected:
- Replace the Engine Control Module (ECM) J623.

Assembly is performed in reverse order of removal, note the following:

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

- End diagnosis and switch the ignition off.