B1397

DTC B1397

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

DTC Descriptor
DTC B1397
- Dimming Reference Voltage Circuit Low

Circuit/System Description

The body control module (BCM) controls the dimming operation of the interior lamps. The BCM applies a 12-volt reference signal to the instrument panel (I/P) dimming switch. When you move the I/P dimming switch, the BCM uses this varying voltage signal in order to apply a pulse width modulation (PWM) voltage which controls the brightness of the interior illumination lamps.

Conditions for Running the DTC

* Voltage supplied to the module is in the normal operating range, approximately 9-16 volts.
* The interior lamps must be ON.

Conditions for Setting the DTC

* The BCM detects a short to ground or an open in the dimming reference voltage circuit.
* The condition is present for longer than 3 ms.

Action Taken When the DTC Sets

The BCM stores DTC B1397 in memory.

Conditions for Clearing the DTC

* A current DTC B1397 clears when the BCM no longer detects an open or a short to ground in the dimming reference voltage circuit.
* A history DTC B1397 clears after 100 consecutive ignition cycles.

Diagnostic Aids

* If the DTC B1397 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics).
* An intermittent short to ground or an open in the following locations may cause an intermittent malfunction to occur:

- The dimming reference voltage circuit
- The I/P dimming switch
- The BCM

Reference Information
Schematic Reference

Interior Lights Dimming Schematics (Interior Lights Dimming Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for Scan Tool Information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition ON, test for 12 volts between the dimming reference voltage circuit terminal 15 and ground.

• If less than the specified range, test the dimming reference voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Verify the scan tool Dimming Control Reference parameter is less than 1 volt.

• If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 13 and the dimming reference voltage circuit terminal 15. Verify the scan tool Dimming Control Reference parameter is greater than 11 volts.

• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the headlamp switch.

Repair Instructions

Perform the after completing the diagnostic procedure.

* Headlamp Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming