The primary purpose of the heater core coolant pump is to circulate engine coolant through the HVAC heater core when heat is required in the cabin for comfort. This normally happens when the vehicle is in an Auto Stop and the mechanical pump is not spinning. If the HVAC control module has determined heat is needed for the cabin, this pump is turned on once the engine is shut off so the customer does not notice a change in heater duct discharge temperatures. The HVAC control module controls the auxiliary coolant pump relay via the heater core coolant pump relay control circuit. Heater core coolant pump relay supplies voltage to the heater core coolant pump.

Control circuit over current

Set heater core pump validity to invalid.

Schematic Reference

Hybrid Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Delivery Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, command the heater core pump ON and OFF with a scan tool.
2. Observe the operation of heater core pump.

1. Disconnect the heater core coolant pump relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the heater core coolant pump relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the heater core coolant pump.
6. Test for less than 5.0 ohms between the heater core coolant pump ground circuit terminal and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the heater core coolant pump.
8. Connect a 15 A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. Verify the heater core coolant pump is activated.

⇒	If the heater core coolant pump does not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the heater core coolant pump.

9. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
10. Command the heater core coolant pump on and off with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

11. If all circuits test normal, test or replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.