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.

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK .

Start diagnosis 

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 Engine Speed (RPM) Sensor -G28- electrical harness connector -5-.

-- Using a multimeter, check the Engine Speed (RPM) Sensor -G28- terminals 2 to 3 for resistance.

Specified value: 0.7 to 1000 kOhm

-- Check 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-. Refer to Engine Mechanical, Fuel Injection & Ignition, Repair Group 13

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-. Refer to ENGINE CONTROL MODULE, REPLACING .

-- 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 T121 terminals for resistance.

Engine Speed (RPM) Sensor -G28- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical harness connector T121 terminals or test box sockets
1	98
1	108
2	82
3	90

Specified value: 1.5 Ω Max.

If the specification was not obtained:

-- Check the wiring for an open circuit, short circuit to each other, Battery (+), and Ground (GND).

-- Check the electrical harness connector for damage, corrosion, loose 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. Refer to Engine Mechanical, Fuel Injection & Ignition, Fuel Injection & Ignition, Repair Group 13.

If the sensor wheel is OK:

-- Erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .

-- Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to READINESS CODE .

-- End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

-- Replace the Motronic Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REPLACING .

-- Assembly is performed in the reverse of the removal.

Final procedures 

After repair work, the following work steps must be performed in the mentioned 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 .