After Boil Coolant Pump Inoperative

After Boil Coolant Pump Inoperative

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) provides 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
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 System Description and Operation (Cooling System)
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 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.

Circuit/System Testing

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

1. Ignition OFF, disconnect the auxiliary coolant pump relay.
2. Ignition ON, verify that a test lamp illuminates between the relay switch ignition circuit and ground.

• If the test lamp does not illuminate, test the relay switch ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch ignition circuit fuse is open, test the appropriate relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the relay.

3. Connect a 10 A fused jumper between the relay switch ignition circuit and the relay controlled output circuit. Verify the pump is activated

• If the pump activates, test or replace the relay.

• If the pump does not activate, test the relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the pump ground circuit for an open/high resistance. If the circuit tests normal, replace the pump.

Component Testing

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

1. Ignition OFF, disconnect the auxiliary coolant pump relay.
2. Test for 70-110 ohm between terminals 85 and 86.

• If not within the specified range, replace the relay.

3. Measure the resistance between the terminals listed below. The DMM should display O.L.

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87

• If not the specified value, replace the relay.

4. Install a 20 A fused jumper wire between B+ and relay terminal 85. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohm of resistance between terminals 30 and 87.

• If greater than the specified value, 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))
* Auxiliary Water Pump Inlet Hose Replacement (Auxiliary Water Pump Inlet Hose Replacement)
* Auxiliary Water Pump Outlet Hose Replacement (Auxiliary Water Pump Outlet Hose Replacement)
* Auxiliary Water Pump Replacement (LLT) (Auxiliary Water Pump Replacement)