Diagnostic Instructions
| • | 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. |
DTC Descriptors
DTC B0484 00: Auxiliary Heater LockedDTC B0485 00: Auxiliary Heater Start Counter Overrun
DTC B0486 00: Auxiliary Heater Cold Blow Time Exceeded
DTC B0488 00: Auxiliary Heater Overheat Counter Overrun
DTC B048A 00: Auxiliary Heater Start Time Exceeded
Circuit/System Description
The coolant heater function is to provide additional heat to the passenger compartment. The coolant heater burns diesel fuel, to heat up the engine coolant when the vehicle is running and will only operate during conditions where ambient temperature is below 4°C (39°F) and a fuel tank level greater than 12.5 percent. The heat of the hot engine coolant is transferred to the HVAC module to heat the passenger compartment. The coolant heater does not heat up instantly. It must go through a self test and start up procedure before normal operation. The vehicle must be running to start the unit but after the unit is no longer commanded on a two minute shut down (purge) procedure starts. The coolant flow is from the engine to the fuel operated heater through the heat exchanger back to the engine. Battery voltage and ground is supplied to the coolant heater. The electronic control unit inside the coolant heater determines when the unit will turn ON and OFF as well as how it will function. The electronic control unit also uses GMLAN communication and the engine control module (ECM) to transfer coolant heater information that the scan tool can read. The fuel operated heater contains flame sensors to disable the glow plug once the flame is established or to abort the startup attempt if the flame is not established.
Conditions for Running the DTC
Engine is running.
Conditions for Setting the DTC
Before every start of the heater, the operation of the individual components is tested.
Action Taken When the DTC Sets
The fuel operated coolant heater is disabled.
Conditions for Clearing the DTC
| • | A current DTC will clear when the conditions for setting the DTC are no longer present. |
| • | A history DTC will clear after 40 malfunction-free ignition cycles. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Air Temperature Description and Operation
Electrical Information Reference
| • | Circuit Testing |
| • | Wiring Repairs |
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, verify DTC B0460 or B0462 is not set.
- If all circuits test normal, replace the coolant heater.
| ⇒ | If either DTC is set, refer to DTC B0460 or B0462 . |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
