B1397

DTC B1397

Circuit 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.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1397 Dimming Reference Voltage Circuit Low

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 MIL/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

Test Description

Step 1 - Step 7:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that the BCM is providing reference voltage to the headlamp switch.
3. This step tests the dimming return circuit for a high resistance or an open.