Auxiliary Engine Coolant Pump Relay Checking

Auxiliary Engine Coolant Pump Relay Checking

Special tools, testers and auxiliary items required

• Multimeter.

• wiring diagrams.

Test requirements

• Fuse (SB15) OK.

• Fuse (SB29) OK.

• The Ground connections at the engine and transmission OK.

• The battery voltage at least 12.5 V.

• The generator OK.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check.

Start diagnosis

- Switch the ignition On.

- Using a multimeter, check the following wiring connection for voltage.






- Switch the ignition Off.

Specified value: 12.5 V

If the specified value was Not obtained:

- Check the Auxiliary Engine Coolant (EC) Pump Relay (J496) socket 1/30 to the Power Supply Relay (terminal 30, B+) (J317) socket 87 for an open circuit, high resistance or short to Ground.

- Check the electrical harness connectors for damage, corrosion, loose or broken terminals.

- If necessary, repair the wiring connection.

If the specified value was obtained:

- Switch the ignition On.

- Using a multimeter, check the following wiring connection for voltage.






- Switch the ignition Off.

Specified value: 12.5 V

If the specified value was Not obtained:

- Check the Auxiliary Engine Coolant (EC) Pump Relay (J496) socket 4/86 to the Power Supply Relay (terminal 30, B+) (J317) socket 87 for an open circuit, high resistance or short to Ground.

- Check the electrical harness connectors for damage, corrosion, loose or broken terminals.

- If necessary, repair the wiring connection.

If the specified value was obtained:

Checking Ground

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 Engine Control Module (ECM) (J623). Refer to the Repair Information.

- Using a multimeter, check the following wiring connection for resistance.






Specified value: 1.5 ohms.

If the specified value was Not obtained:

- Check the Auxiliary Engine Coolant (EC) Pump Relay (J496) socket 85 to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T121 terminal 48 for an open circuit, high resistance or a short to Battery (+).

- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring and the voltage supply was OK:

- Replace the Auxiliary Engine Coolant (EC) Pump Relay (J496).

- Perform a road test to verify repair.

If the fault does not return:

Generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.

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

- Replace the Engine Control Module (ECM) (J623). Refer to the Repair Information.

- Assembly is performed in the reverse of the 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 ] Diagnostic Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.