Engine Speed Sensor, Checking

The Engine Speed (RPM) Sensor -G28- provides the engine speed signal. If the Engine Speed (RPM) Sensor -G28- fails, the engine continues to run using a back up signal from the Needle Lift Sensor -G80-.

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements 

• The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248- fuses OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• 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.

Test procedure 

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

Start diagnosis 

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

Checking internal resistance

-- Using a multimeter, check the Engine Speed (RPM) Sensor -G28- terminals 1 to 2 for resistance.

Specified value: 0.7 to 1000k Ω.

-- Check Engine Speed (RPM) Sensor -G28- terminals 1 to 3 and 2 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 68 PIN TEST BOX ADAPTER, INSTALLING .

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

-- Remove the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-. Refer to ENGINE CONTROL MODULE, REPLACING .

-- Using a Multimeter --, check the Engine Speed (RPM) Sensor -G28- electrical harness connector terminals to the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248- electrical harness connector T60 terminals for an open circuit.

Engine Speed (RPM) Sensor -G28- electrical harness connector terminals	Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248- electrical harness connector T60 terminals or test box socket
1	58
2	43
3	Ground (GND)

Specified value: 1.5 Ω 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, 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.

If the sensor wheel is OK:

-- Replace the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-. Refer to ENGINE CONTROL MODULE, REPLACING .

Final procedures 

After the 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