After Boil Coolant Pump Always On

After Boil Coolant Pump Always On

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic procedure.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of the diagnostic category.

Circuit/System Description

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.

Diagnostic Aids

The auxiliary coolant or after boil pump relay may be referred to as "ENG PUMP" or "FUEL COOL" on the underhood electrical center (UBEC) cover label.

Reference Information
Schematic Reference

Engine Cooling Schematics ([1][2]Cooling System)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Cooling Fan Description and Operation (Cooling Fan)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

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 (P2600).

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.

Circuit/System Testing

Note: The UBEC label may refer to this relay as the ENG PUMP or FUEL COOL relay.

1. Ignition OFF, disconnect auxiliary coolant pump 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.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))