Engine Speed Sensor, Checking

Special tools and workshop equipment 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 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 Ω (at approx. 20° 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)

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 Wiring and Components, Checking with Test Box VAG 1598/42 . .

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

-- Remove the Motronic Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REMOVING AND INSTALLING .

-- 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 T60a terminals for an open circuit.

Engine Speed (RPM) Sensor -G28- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical connector T60a terminals or test box sockets
1	26
2	36
3	51

Specified value: 1.5 Ω 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-. Refer to ENGINE CONTROL MODULE, REMOVING AND INSTALLING .

Assembly is performed in the reverse order of removal.

Final procedures 

After 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 .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .

-- End of diagnosis.