Diagnostic Instructions
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
| • | An intermittent short to ground or an open in the following locations may cause an intermittent malfunction to occur: |
| - | The dimming reference voltage circuit |
Reference Information
Schematic Reference
Interior Lights Dimming Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
Scan Tool Reference
Control Module References for Scan Tool Information
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the headlamp switch.
- 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. |
- 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. |
- 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. |
- If all circuits test normal, test or replace the headlamp switch.
Repair Instructions
Perform the after completing the diagnostic procedure.
