Pinpoint Test F: The Auxiliary Heater Control Module (AHCM) Does Not Respond To The Scan Tool

Communications Network

Pinpoint Test F: The Auxiliary Heater Control Module (AHCM) Does Not Respond To The Scan Tool


Normal Operation

The Auxiliary Heater Control Module (AHCM) is optional equipment on diesel engine vehicles only. The AHCM (Auxiliary Heater Control Module) communicates with the scan tool through the High Speed Controller Area Network (HS-CAN).

This pinpoint test is intended to diagnose the following:

- Fuse

- Wiring, terminals or connectors

- AHCM (Auxiliary Heater Control Module)

PINPOINT TEST F : THE AHCM (Auxiliary Heater Control Module) DOES NOT RESPOND TO THE SCAN TOOL

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

NOTE: Failure to disconnect the battery when instructed will result in false resistance readings.

F1 CHECK THE AHCM (Auxiliary Heater Control Module) VOLTAGE SUPPLY CIRCUIT FOR AN OPEN

- Disconnect: AHCM (Auxiliary Heater Control Module) C2463B.

- Ignition ON.

- Measure the voltage between the AHCM (Auxiliary Heater Control Module) C2463B-1, circuit CBP37 (WH), harness side and ground.





Is the voltage greater than 10 volts?

Yes
GO to F2.

No
VERIFY the Body Control Module (BCM) fuse 37 (10A) is OK. If OK, REPAIR the circuit in question. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. CLEAR the DTCs. REPEAT the network test with the scan tool. [1][2]Diagrams By Number

F2 CHECK THE AHCM (Auxiliary Heater Control Module) GROUND CIRCUIT FOR AN OPEN

- Ignition OFF.

- Disconnect: Negative Battery Cable.

- Disconnect: AHCM (Auxiliary Heater Control Module) C2463A.

- Measure the resistance between the AHCM (Auxiliary Heater Control Module) C2463A-1, circuit GD108 (BK), harness side and ground.





Is the resistance less than 5 ohms?

Yes
GO to F3.

No
REPAIR the circuit. CLEAR the DTCs. REPEAT the network test with the scan tool.

F3 CHECK THE HS-CAN (High Speed Controller Area Network) CIRCUITS BETWEEN THE AHCM (Auxiliary Heater Control Module) AND THE DLC (Data Link Connector) FOR AN OPEN

- Measure the resistance between the AHCM (Auxiliary Heater Control Module) C2463B-3, circuit VDB04 (WH/BU), harness side and the Data Link Connector (DLC) C251-6, circuit VDB04 (WH/BU), harness side.





- Measure the resistance between the AHCM (Auxiliary Heater Control Module) C2463B-4, circuit VDB05 (WH), harness side and the DLC (Data Link Connector) C251-14, circuit VDB05 (WH), harness side.





Are the resistances less than 5 ohms?

Yes
CONNECT the negative battery cable. GO to F4.

No
REPAIR the circuit in question. CLEAR the DTCs. REPEAT the network test with the scan tool.

F4 CHECK FOR CORRECT AHCM (Auxiliary Heater Control Module) OPERATION

- Disconnect all the AHCM (Auxiliary Heater Control Module) connectors.

- Check for:
- corrosion

- damaged pins

- pushed-out pins


- Connect all the AHCM (Auxiliary Heater Control Module) connectors and make sure they seat correctly.

- Operate the system and verify the concern is still present.

Is the concern still present?

Yes
INSTALL a new AHCM (Auxiliary Heater Control Module). CLEAR the DTCs. REPEAT the network test with the scan tool.

No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.