B257B
DTC B257B
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC B257B 03
-
Lighting Control Switch Signal Low Voltage
DTC B257B 07
-
Lighting Control Switch Signal High Voltage
Diagnostic Fault Information
Circuit/System Description
The body control module (BCM) supplies a reference voltage to the backlight dimmer switch, which is part of the headlamp switch. When the backlight dimmer switch is placed in a desired brightness position, reference voltage is applied through the backlight dimmer switch rheostat to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage to the LED dimming supply circuit to all related interior lamps, illuminating them to the desired level of brightness.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
B257B 03
The BCM detects a voltage that is lower than 0.3 V on the dimming voltage circuit.
B257B 07
The BCM detects a voltage that is greater than 12.2 V on dimming voltage circuit.
Action Taken When the DTC Sets
The BCM will not dim or illuminate any LED backlighting supplied by the backlight lamp control circuits.
Conditions for Clearing the DTC
* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 100 consecutive malfunction ignition cycles have occurred.
Reference Information
Schematic Reference
Interior Lights Dimming Schematics Interior Lights Dimming Schematics
Connector End View Reference
Component Connector End Views Sunshade - Left (DH6)
Description and Operation
Interior Lighting Systems Description and Operation Interior Lighting Systems
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References
Circuit/System Verification
Ignition ON, switch ON exterior lighting, vary the interior backlight from dim to full bright by using the dimmer switch. The interior backlighting should dim and then become full bright.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the S30 Headlamp Switch.
2. Ignition ON, test for B+ between the 12 V reference circuit terminal 1 and ground.
• If less than the specified range, test the 12 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.
3. Ignition ON, test for less than 0.3 V between dimming signal circuit terminal 12 and ground.
• If greater than the specified range, test the dimming signal circuit terminal 12 for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module.
4. Reconnect the harness connector at the S30 Headlamp Switch.
5. Dim the interior backlighting with the S30 Headlamp Switch.
6. Disconnect the harness connector at the S30 Headlamp Switch.
7. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the voltage reference circuit terminal 1. The interior backlighting should now be dimmed.
• If the interior backlighting is not dimmed, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.
8. If all circuits test normal, replace the S30 Headlamp Switch.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Headlamp Switch Replacement Service and Repair
* Control Module References Control Module References for BCM replacement, setup, and programming