Volt

DTC B0468, B046B, or B046C

The auxiliary heater coolant pump is controlled with a pulse-width modulated control sent from the HVAC control module to the auxiliary heater coolant pump. The higher the duty cycle on the control the higher the pump speed. An enable signal from the HVAC control module to the auxiliary heater coolant pump provides overall control of the pump. When voltage is present, the pump can operate. The auxiliary heater coolant pump provides a hard-wired pulse-width modulated feedback signal to the HVAC control module. During normal operation, this feedback signal provides pump speed information.

B0468 01

B0468 06

B046B 00

B046C 02

B046C 05

B0468 01

Requested PWM is not zero and the feedback from the Auxiliary Heater is always High.

B0468 06

Feedback from the auxiliary heater voltage is always low or floating.

B046B 00

PWM duty cycle/frequency out of range

B046C 02

PWM duty cycle/frequency out of range

B046B 05

PWM duty cycle/frequency out of range

The auxiliary heater coolant pump is disabled.

B0468 01

Feedback of auxiliary heater output corresponds with requested PWM signal.

B0468 06

Feedback of auxiliary heater output corresponds with requested PWM signal.

B046B 00

PWM duty cycle/frequency is within defined range

B046C 02

Requested status of the output is ON and feedback shows normal operation

B046B 05

Requested status of the output is OFF and feedback shows normal operation

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Vehicle in Service Mode, HVAC system turned ON, with a scan tool, verify that the Auxiliary Heater Coolant Pump Command is between 20%-90% and Auxiliary Heater Coolant Pump Feedback is about 50%

1. Vehicle OFF, disconnect the harness connector at the G36 auxiliary heater coolant pump.
2. Vehicle OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.
3. Test for less than 10 Ω between the ground circuit terminal 4 and ground.

⇒	If 10 Ω or greater

3.1.	Vehicle OFF.

3.2.	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

4. Vehicle ON, verify a test lamp illuminates between the B+ circuit terminal 5 and ground.

⇒	If the test lamp does not illuminate and the circuit fuse is good

4.1.	Vehicle OFF.

4.2.	Test for less than 2 Ω in the B+ circuit end to end.

⇒	If 2 Ω or greater, repair the open/high resistance in the circuit.

⇒	If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.

⇒	If the test lamp does not illuminate and the circuit fuse is open

4.1.	Vehicle OFF.

4.2.	Test for infinite resistance between the B+ circuit and ground.

⇒	If less than infinite resistance, repair the short to ground on the circuit.

⇒	If infinite resistance, replace the G36 auxiliary heater coolant pump..

⇓	If the test lamp illuminates

5. Vehicle ON, connect a test lamp between the enable circuit terminal 1 and the ground circuit terminal 4.
6. Verify the test lamp turns ON and OFF when Commanding the Auxiliary Coolant Pump Speed Command ON and OFF with a scan tool.

⇒	If the test lamp is always OFF

6.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.

6.2.	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

6.3.	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 K33 HVAC control module.

⇒	If the test lamp is always ON

6.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module, vehicle ON.

6.2.	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 K33 HVAC control module.

⇓	If the test lamp turns ON and OFF

7. Connect a DVOM between the control circuit terminal 3 and the enable circuit terminal 1.
8. Verify the voltage changes when Commanding the Auxiliary Coolant Pump Speed Command ON and OFF with a scan tool.

⇒	If the voltage stays below 3 volts while commanding ON and OFF

8.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.

8.2.	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

8.3.	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 K33 HVAC control module.

⇒	If the voltage stays greater than 11 volts while commanding ON and OFF

8.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module, vehicle ON.

8.2.	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 K33 HVAC control module.

⇓	If the voltage is 0 volts OFF and 12 volts ON while commanding ON and OFF

9. Verify the scan tool Auxiliary Coolant Pump Speed Feedback Frequency parameter is less than 10%.

⇒	If greater than 10%

9.1.	Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.

9.2.	Test for infinite resistance between the signal circuit terminal 2 and ground.

⇒	If less than infinite resistance, repair the short to ground on the circuit.

⇒	If infinite resistance, replace the K33 HVAC control module.

⇓	If 10% or less

10. Install a 3 A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 4.
11. Verify the scan tool Auxiliary Coolant Pump Speed Feedback Frequency parameter is greater than 90%.

⇒	If less than 90%

11.1.

Vehicle OFF, disconnect the harness connector at the K33 HVAC control module, vehicle ON.

11.2.

Test for less than 1 V between the signal circuit terminal 2 and ground.

⇒	If 1 V or greater, repair the short to voltage on the circuit.

⇓	If less than 1 V

11.3.

Vehicle OFF

11.4.

Test for less than 2 Ω in the signal circuit end to end.

⇒	If 2 Ω or greater, repair the open/high resistance in the circuit.

⇒	If less than 2 Ω, replace the K33 HVAC control module.

⇓	If 90% or greater

12. If all circuits test normal, test or replace the G36 auxiliary heater coolant pump.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.