Engine Speed Sensor: Testing and Inspection

Engine Speed (RPM) Sensor G28, Checking

Special tools, testers and auxiliary items required
- Multimeter V.A.G 1526 or equivalent.
- Test Box 105 Pin VAG1598/42.
- Adapter Lead Vag1598/39 VAG1598/39.
- Adapter cable V.A.G 1598/39-1.

NOTE: 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.

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 diagnostic tester.
- 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.







- Using multimeter V.A.G 1526 B or equivalent, check Engine Speed (RPM) Sensor G28 electrical connector terminals 2+3 for resistance.
Specified value: 730 to 1000 Ohms (at approx. 20 degrees C)







- Using multimeter V.A.G 1526 B or equivalent, check Engine Speed (RPM) Sensor G28 for short circuit between terminals 1 + 2 as well as 1 + 3.
Specified value: 0 Ohms

If specification is not obtained:
- Replace Engine Speed (RPM) Sensor G28.

If specification is obtained:
- Connect the Test Box 105 Pin VAG1598/42 to the wiring harness of the Engine Control Module (ECM) J623.







- Using the Test Box 105 Pin VAG1598/42 and Multimeter V.A.G 1526 A or equivalent, check the following wiring connection for an open circuit.

Terminal Test box socket
1 52
2 51
3 36

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 specification is obtained:
- Replace the Engine Control Module (ECM) J623.

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.