After Boil Coolant Pump Malfunction

After Boil Coolant Pump Malfunction

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 approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provide an overview of each 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
Description and Operation

Cooling System Description and Operation (Cooling System)
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 DTC is set, repair the DTC first. Refer to DTC P2600-P2603 (P2600).

2. Ignition ON, command the auxiliary coolant pump relay ON and OFF with a scan tool. Verify that the pump turns ON and OFF when changing between the commanded states.

• If the auxiliary coolant pump does not activate, refer to After Boil Coolant Pump Inoperative (After Boil Coolant Pump Inoperative).

Circuit/System Testing

1. Test for a blockage or restriction in the auxiliary coolant pump lines and hoses.
2. Test the pump coolant passage for a blockage or a restriction.
3. Test the pump impeller for a seized or binding condition.

Repair Instructions

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

* Auxiliary Water Pump Replacement (LLT) (Auxiliary Water Pump Replacement)
* Auxiliary Water Pump Inlet Hose Replacement (Auxiliary Water Pump Inlet Hose Replacement)
* Auxiliary Water Pump Outlet Hose Replacement (Auxiliary Water Pump Outlet Hose Replacement)