Pinpoint Test V: The Electric Heater is Inoperative/Does Not Operate Correctly

Climate Control System

Pinpoint Tests

Pinpoint Test V: The Electric Heater is Inoperative/Does Not Operate Correctly

Refer to Wiring Diagram Set 54, Manual Climate Control System for schematic and connector information. Diagrams By Number

Refer to Wiring Diagram Set 55, Automatic Climate Control System for schematic and connector information. Diagrams By Number

NOTE: Coolant temperature is critical for heater performance. Diesel engines warm up more slowly than gasoline engines, especially if idling or under light engine loads. Under these conditions, cab heat will not be at peak performance. The diesel electric heater option is designed to provide cab heat during the normal extended warm-up period.

Normal Operation

Under normal operation, the Auxiliary Heater Control Module (AHCM) receives a ground through circuit GD108 (BK/VT)/ZE008 (BK). The AHCM is supplied constant battery voltage through circuit SDC02 (RD)/SDF03 (RD) and ignition switched voltage through circuit CBP37 (WH).

This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- AHCM



PINPOINT TEST V: THE ELECTRIC HEATER IS INOPERATIVE/DOES NOT OPERATE CORRECTLY

NOTE: Make sure that conditions for the operation of the electric heater are met. Refer to Electric Heater in Description and Operation.

NOTE: Before beginning this test, make sure coolant engine coolant temperature is below 85°C (185°F). If the coolant temperature is above 85°C (185°F), the AHCM will not operate.

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V1 CHECK AHCM CURRENT BY MONITORING THE AUXILIARY HEATER CURRENT (AHCM_CUR) AHCM PID


- Ignition ON.
- Enter the following diagnostic mode on the scan tool: AHCM_CUR AHCM PID.
- Select the warmest setting on the HVAC module.
- Select the highest blower setting on the HVAC module.
- With the engine running, monitor the AHCM_CUR AHCM PID.
- Is the AHCM_CUR PID read greater than 50 amps?

Yes
The system is operating correctly at this time.

No
GO to V2.

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V2 CHECK AHCM VOLTAGE BY MONITORING THE AUXILIARY HEATER VOLTAGE (AHCM_V) AHCM PID


- Enter the following diagnostic mode on the scan tool: AHCM_V AHCM PID.
- Select the warmest setting on the HVAC module.
- Select the highest blower setting on the HVAC module.
- With the engine running, monitor the AHCM_V AHCM PID.
- Is the AHCM_V PID read less than 12 volts?

Yes
INSPECT circuit SDC02 (RD)/SDF03 (RD) or ZE008 (BK)/GD108 (BK/VT) for excessive resistance such as a loose, corroded or damaged connector or wire. REPAIR as necessary. TEST the system for normal operation.

No
INSTALL a new AHCM. REPEAT the self-test. TEST the system for normal operation.

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