After Boil Coolant Pump Always On for Cadillac STS 2008

The auxiliary coolant pump system provides a measure of prevention against fuel vaporization due to excessive engine temperatures. The engine control module (ECM) commands the auxiliary or after boil coolant pump On when the engine coolant temperature exceeds a calibrated value. The ECM applies ground to the coil side of the auxiliary pump relay. This energizes the coil and applies voltage directly to the pump motor through the switch side of the relay.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Verify that DTCs P2600, P2602 and P2603 are not set.

⇒	If any auxiliary coolant pump DTCs are set, repair the DTC first. Refer to DTC P2600-P2603 .

2. Ignition ON, verify with a scan tool that the ECM is not commanding pump activation.
3. Ignition ON, observe that the pump is not activated.

1. Ignition OFF, disconnect FUEL COOL relay.
2. Ignition ON, observe that the auxiliary coolant pump is not activated.

⇒	If the pump is activated, test for a short to voltage in the relay controlled output circuit.

⇒	If the pump is not activated, test or replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement