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 System 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 DTC is set, repair the DTC first. Refer to DTC P2600-P2603.

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.

1. Ignition OFF, disconnect the FUEL COOL 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.

1. Ignition OFF, disconnect the auxiliary coolant pump relay.
2. Test for 70-110 Ω 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 Ω of resistance between terminals 30 and 87.

⇒	If greater than the specified value, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.