Auxiliary Water Pump Relay: Testing and Inspection

Recirculation Pump, Voltage Supply, Checking

The voltage supply for the Recirculation Pump V55 may be supplied by either the Recirculation Pump Relay J160 or the Residual Heat Relay J708

Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.

Test requirements
- The Residual Heat Relay J708 fuse OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, selector lever in position "P" or "N" .
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Test sequence

Checking voltage
- Switch the ignition on.
- Using a Multimeter , check for power at Pin 1 of V55 and chassis ground.

Specified value: battery voltage.
- Switch the ignition off.

If the specified value was not obtained:
- Check the wiring connection from the Plus 30 Terminal Connection (SB2 Fuse Panel B) to the Residual Heat Relay socket 3/30 for an open circuit or a short circuit.
- Check the wiring connections for damage, corrosion, loose or broken terminals.
- If necessary, repair the faulty wiring connection.

If the specified value was obtained:
- Switch the ignition on.
- Using a Multimeter , check the Residual Heat Relay socket 1/86 to Ground (GND).

Specified value: battery voltage.

- Switch the ignition off.

If the specified value was not obtained:
- Check the wiring connection from the Residual Heat Relay socket 2/85 to Climatronic Control Module J255 , connector T24, Pin 14.
- Check the wiring connections for damage, corrosion, loose or broken terminals.
- If necessary, repair as needed.
- Using a Multimeter, check the Residual Heat Relay J708 socket 2/85 to chassis ground (GND).

If the specified value (Approx 2 ohms) was obtained,
- Replace Recirculation Pump Relay J160 or the Residual Heat Relay J708

If no malfunction is found in the wiring and voltage supply at Residual Heat Relay J708 socket 1/86 was not OK:

- Check or replace Climatronic Control Module J255

Final procedures
After repair work, the following work steps must be performed in the following sequence:
1. Check the 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.