Service Information

Cruze

DTC B257B

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	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	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Dimming 12V Reference	B257B 03*	B257B 03*	--	--
Instrument Panel Lamps Dimmer Switch Signal	B257B 03*	B257B 03*	B257B 07*	-
* Interior Backlighting at Full Intensity And Cannot be Dimmed

The body control module (BCM) supplies a reference voltage to the dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the 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

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, 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

Ignition OFF, disconnect the harness connector at the S30 Headlamp Switch.
Ignition ON, test for greater than 11 V between the 12 V reference circuit terminal 1 and ground.

⇒	If greater than the specified range, test the 12 V reference circuit for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module.

⇒	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.

Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.3 V.

⇒	If greater than the specified range, test the signal circuit terminal 12 for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module.

Install a 3 A fused jumper wire between the signal circuit terminal 12 and the voltage reference circuit terminal 1. Verify the scan tool Dimming Control Signal parameter is greater than 11.7 V.

⇒	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 K9 Body Control Module.

If all circuits test normal, replace the S30 Headlamp Switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•	Headlamp Switch Replacement

•	Control Module References for BCM replacement, setup, and programming