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 in order to control the brightness of the interior illumination lamps.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B1398 Dimming Reference Voltage Circuit High
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating range, approximately 10-16 volts. |
| • | The interior lamps must be ON. |
Conditions for Setting the DTC
| • | The BCM detects a short to battery positive voltage 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 B1398 in memory.
Conditions for Clearing the MIL/DTC
| • | A current DTC B1398 clears when the BCM no longer detects a short to battery positive voltage in the dimming reference voltage circuit. |
| • | A history DTC B1398 clears after 100 consecutive ignition cycles. |
Diagnostic Aids
| • | If the DTC B1398 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections . |
| • | An intermittent short to battery positive voltage 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
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the dimming reference circuit for a short to battery positive voltage.
-
This step tests the dimming return circuit for a short to battery positive voltage.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Interior Lights Dimming Schematics Connector End View Reference: Master Electrical Component List | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
Does the voltage measure near the specified value? | 12 V | Go to Step 4 | Go to Step 3 | |
Test the dimming return circuit for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 | |
4 | Test the dimming reference voltage circuit for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 5 |
5 | Replace the body control module (BCM). Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 7 | -- |
6 | Replace the headlamp switch. Refer to Headlamp Switch Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- |
7 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
