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) J220 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:

Checking internal resistance







- Disconnect the gray Engine Speed (RPM) Sensor G28 electrical harness connector - 3 -.
- Using a multimeter , check the Engine Speed (RPM) Sensor G28 terminals 2 to 3 for resistance.
Specified value: 730 to 1000 Ohms (at approx. 20 degrees C)







- Check 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) J220.







- Using a Multimeter , check the Engine Speed (RPM) Sensor G28 electrical harness connector terminals to the Motronic Engine Control Module (ECM) J220 electrical harness connector terminals for an open circuit.

Engine Speed (RPM) Sensor Motronic Engine Control Module
G28 electrical harness (ECM) J220 electrical connector
connector terminals test box socket
1 108
2 90
3 82

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, 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) J220.

Final procedures
After the 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.




With Manufacturer's V.A.G 1598/31 Test Box

Engine Speed (RPM) Sensor -G28-, Checking







Special tools and workshop equipment required
- V.A.G 1526 A Multimeter
- V.A.G 1594 A Connector test kit
- V.A.G 1598/31 Test box

NOTE: The engine speed (RPM) sensor is a combined speed sensor and reference mark sensor. The engine cannot be started without a signal from the Engine speed (RPM) sensor -G28-. If the signal from the Engine speed (RPM) sensor -G28- fails while the engine is running, the engine will cut out immediately.

Work sequence
- Before performing test, make sure that sensor is correctly installed and firmly seated.







- Disconnect Engine speed (RPM) sensor connector -G28- -Pos. 3-.







NOTE: To gain access to the connector, remove coolant expansion tank bolt (arrow) and move expansion tank to the side. Fuel hoses remain connected.







- Connect multimeter between terminals 2 and 3 to measure resistance.
- Specified value: 730...1000 Ohms

NOTE: The resistance value of the Engine speed (RPM) sensor -G28- is associated with a temperature of 20 degrees C. The resistance increases if the temperature increases.

If specified value is not obtained:
- Install new Engine speed (RPM) sensor -G28-.

If specified value is obtained:







- Connect multimeter between terminals 2 and 1 -screen- and 3 and 1 -screen- to measure resistance.
- Specified value: each case infinity ohm (no continuity)

If specified value is not obtained:
- Install a new Engine speed (RPM) sensor -G28-.

If specified value is obtained:
- Connect test box V.A.G 1598/31 to wiring harness for ECM; do not connect ECM.







- Check for open circuit, short to positive, or short to ground in following wiring connections:

Connector Test box V.A.G 1598/31
terminal Socket
1 (screening) 108
2 (ground) 90
3 (signal) 82

- Repair any open/short circuit as necessary.

If no wiring problems are found:
- Replace ECM.