PRE-RELEASE
DTC B257B
| DTC B257B |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
has overviews of all diagnostic categories.
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| DTC Descriptors |
DTC B257B 03
Lighting Control Switch Signal Low Voltage
DTC B257B 07
Lighting Control Switch Signal High Voltage
| Diagnostic Fault Information |
| Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
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Dimming 12V Reference
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B257B 03*
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B257B 03*
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Instrument Panel Lamps Dimmer Switch Signal
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B257B 03*
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B257B 03*
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B257B 07*
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* Interior backlighting at full intensity and cannot be dimmed.
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| 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 resistor ladder 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 |
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All cluster/backlighting defaults full bright.
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Steering wheel controls inoperative.
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Front and rear fog lamps are inoperative.
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| Conditions for Clearing the DTC |
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The condition responsible for setting the DTC no longer exists.
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A history DTC will clear once 100 consecutive malfunction ignition cycles have occurred.
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| Reference Information |
Schematic Reference
Interior Lights Dimming Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Interior Lighting Systems Description and Operation
Electrical Information Reference
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Circuit Testing
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Connector Repairs
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Testing for Intermittent Conditions and Poor Connections
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Wiring Repairs
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Scan Tool Reference
Control Module References for information on diagnostic tools
| 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.
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| 2. |
Ignition ON, test for B+ between the 12 V reference circuit terminal 1 and ground.
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| 3. |
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.
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Ignition ON, test for less than 0.3 V between dimming signal circuit terminal 12 and ground.
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| 5. |
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.
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Reconnect the harness connector at the S30 Headlamp Switch.
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Dim the interior backlighting with the S30 Headlamp Switch.
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| 8. |
Disconnect the harness connector at the S30 Headlamp Switch.
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| 9. |
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.
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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.
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| 11. |
If all circuits test normal, replace the S30 Headlamp Switch.
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| Repair Instructions |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
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Headlamp Switch Replacement
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Control Module References
for information on BCM replacement, setup, and programming
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