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

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, a request is sent via serial data to the engine control module to turn the pump ON. The engine control module controls the auxiliary coolant pump relay via the heater core coolant pump relay control circuit. The heater core coolant pump relay supplies voltage to the heater core coolant pump.

• The 12 V battery voltage is greater than or equal to 9 V.
• The auxiliary heater coolant pump enable is commanded.

The engine control module detects the auxiliary heater coolant pump relay control circuit is open, shorted to voltage or shorted to ground.

DTCs B269A, B269C, and B269D are type B DTCs.

DTCs B269A, B269C, and B269D are type B DTCs.

HVAC Schematics

Master Electrical Component List

Manual HVAC Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

1. Ignition OFF, disconnect the X3 harness connector at the X50A Fuse Block– Underhood.
2. Connect a test lamp between the control circuit terminal 17 and B+, ignition ON.
3. Verify the test lamp turns ON and OFF when commanding the G36  Auxiliary Heater Coolant Pump On and Off with a scan tool.
• If the test lamp is always OFF
1. Ignition OFF, remove the test lamp, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Ignition OFF.
4. Test for less than 2 Ω in the control circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the K20 Engine Control Module.
• If the test lamp is always ON
1. Ignition OFF, remove the test lamp, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the K20 Engine Control Module.
• If the test lamp turns ON and OFF
4. Ignition OFF and all vehicle systems OFF, connect the X3 harness connector at the X50A Fuse Block– Underhood. Disconnect the harness connector at the G36 Auxiliary Heater Coolant Pump. It may take up to 2 min for all vehicle systems to power down.
5. Test for less than 10 Ω between the ground circuit terminal 1 and ground.
• If 10 Ω or greater
1. Ignition OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, repair the open/high resistance in the ground connection.
• If less than 10 Ω
6. Connect a test lamp between the control circuit terminal 2 and ground.
7. Verify the test lamp turns ON and OFF when commanding the G36 Auxiliary Heater Coolant Pump ON and OFF with a scan tool.
• If the test lamp is always OFF and the circuit fuse is good
1. Ignition OFF, remove the test lamp, disconnect the X3 harness connector at the X50A Fuse Block– Underhood.
2. Test for less than 2 Ω in the control circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the X50A Fuse Block– Underhood.
• If the test lamp is always OFF and the circuit fuse is open
1. Ignition OFF, remove the test lamp.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, test or replace the G36 Auxiliary Heater Coolant Pump.
• If the test lamp is always ON
1. Ignition OFF, disconnect the X3 harness connector at the X50A Fuse Block– Underhood, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the X50A Fuse Block– Underhood.
• If the test lamp turns ON and OFF
8. Test or replace the G36 Auxiliary Heater Coolant Pump.

Perform the Diagnostic Repair Verification after completing the repair.

• HVAC Component Replacement Reference
• Control Module References for control module replacement, programming and setup