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

Climate Control System

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

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 Is not at peak performance. The diesel electric heater option is designed to provide cab heat during this normal extended warm-up period.

Normal Operation

Under normal operation, the Auxiliary Heater Control Module (AHCM) receives a ground through circuit GD108 (BK). The AHCM (Auxiliary Heater Control Module) is supplied constant battery voltage through circuit SDF05 (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 (Auxiliary Heater Control Module)

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

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

S1 CHECK AHCM (Auxiliary Heater Control Module) CURRENT BY MONITORING THE AUXILIARY HEATER CURRENT (AHCM_CUR) AHCM (Auxiliary Heater Control Module) PID

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 (Auxiliary Heater Control Module) will not operate.

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: AHCM_CUR AHCM (Auxiliary Heater Control Module) 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 (Auxiliary Heater Control Module) PID.

Is the AHCM_CUR PID read greater than 50 amps?

Yes
The system is operating correctly at this time.

No
GO to S2.

S2 CHECK AHCM (Auxiliary Heater Control Module) VOLTAGE BY MONITORING THE AUXILIARY HEATER VOLTAGE (AHCM_V) AHCM (Auxiliary Heater Control Module)
PID

- Enter the following diagnostic mode on the scan tool: AHCM_V AHCM (Auxiliary Heater Control Module) 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 (Auxiliary Heater Control Module) PID.

Is the AHCM_V PID read less than 12 volts?

Yes
INSPECT circuit SDF05 (RD) or GD108 (BK) 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 (Auxiliary Heater Control Module). REPEAT the self-test. TEST the system for normal operation.