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Home >> GMC >> 2011 >> Terrain SLT, 2.4 C, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 178 (Lighting System) >> Diagnostic Information and Procedures >> DTC B257B >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Terrain and 2010 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the S36 instrument panel dimmer switch.
  2. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 5 and ground.
    • If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.
    • If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  3. Ignition ON, test for less than 0.3 V between dimming signal circuit terminal 9 and ground.
    • If greater than the specified range, test the dimming signal circuit terminal 9 for a short to voltage. If the circuit tests normal, replace the K9 BCM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal 9 and the voltage reference circuit terminal 5. 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 BCM.
  5. If all circuits test normal, replace the S36 instrument panel dimmer switch.
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