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DTC 91

DTC 91

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 Descriptor

DTC 91

Parking Heater External Interference Voltage

Circuit/System Description

The parking heater does not heat up instantly. It must go through a self test and start up procedure before normal operation. The parking heater depends on the fuel pump to deliver enough fuel in a timely manner. The electronic control module inside the heater determines when to turn on the fuel pump and the glow plug by monitoring coolant temperature and combustion temperature. The combustion sensor disables the glow plug once combustion is established and aborts the startup process if combustion is not established.

Conditions for Running the DTC

Ignition OFF. Battery voltage must be between 10-15 V.

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 parking heater will lock.

Conditions for Clearing the DTC

DTC must be cleared with the remote control.

Diagnostic Aids

Ensure that all power related DTCs are diagnosed and corrected prior to diagnosing this DTC.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Fuel Operated Heater Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Circuit/System Verification

Ignition OFF, command the independent heater ON and OFF with the remote control. Verify the independent heater turns ON and OFF with no DTCs.

Circuit/System Testing


1. Attempt to clear the DTC with the remote control.

2. Ensure that there are no high amperage circuits near the parking heater circuits.

3. If all circuits test normal and the DTC will not clear, replace the K87 Parking Heater Control Module.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.