GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 SRX 🢒 Body Systems 🢒 Lighting 🢒 DTC B257A

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 the diagnostic category.

DTC Descriptor

DTC B257A 00: Headlamp Switch Input Signals Mismatch

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Flash to Pass Switch Signal

1

1

1

--

Headlamp High Beam Relay Control

1

1

B2580 00, 1

--

Headlamp Low Beam Relay Control

1

1

B2575 00, 1

--

Headlamp Switch High Beam Signal

1

1

1

--

Headlamp Switch Headlamps ON Signal

B257A 00, 1

1

1

--

Headlamp Switch Headlamps OFF Signal

B257A 00, 1

1

1

--

Park Lamp Switch Signal

2

2

2

--

LF High Beam Headlamp Voltage Supply

1

1

1

--

LF Low Beam Headlamp Voltage Supply

1

1

1

--

RF High Beam Headlamp Voltage Supply

1

1

1

--

RF Low Beam Headlamp Voltage Supply

1

1

1

--

LF Headlamp Ground

--

1

--

--

RF Headlamp Ground

--

1

--

--

Turn Signal/Multifunction Switch Ground

--

1, 2

--

--

  1. Headlamps Malfunction
  2. Park, License, and/or Tail Lamps Malfunction

Circuit/System Description

When the turn signal/multifunction switch is placed in the AUTO position, the body control module (BCM) receives a ground signal through the headlamp switch headlamps OFF signal circuit. The turn signal/multifunction switch headlamps ON signal circuit and the park lamp switch signal circuit are both open and have no ground signal. When the turn signal/multifunction switch is placed in the PARK or HEAD position, the BCM will receive a ground signal through the headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit. The headlamp switch headlamps OFF signal circuit will be open and have no ground signal. For more detailed information concerning headlamp operation refer to Exterior Lighting Systems Description and Operation .

Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

DTC B257A 00 will set when the BCM detects a short to ground on the headlamp switch headlamps OFF signal circuit or the headlamp switch headlamps ON signal circuit.

Actions Taken When the DTC Sets
    • When DTC B257A 00 is present on the headlamp switch headlamps OFF signal circuit, the low beam headlamps are always ON in the AUTO position. The headlamp switch operates in all positions other than AUTO. The AUTO headlamp defeat is inoperative.
    • When DTC B257A 00 is present on the headlamp switch headlamps ON signal circuit, the low beam headlamps are always ON. The BCM disregards all headlamp switch inputs.

Conditions for Clearing the DTC
    • The condition responsible for setting the DTC no longer exists.
    • You issue a scan tool CLEAR DTCs command.
    • A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Testing
  1. Ignition OFF, disconnect the C1 and C2 harness connectors at the BCM.
  2. Connect a test lamp between the headlamp switch OFF signal circuit and B+.
  3. Turn the headlamp switch to the ON and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
    4. ⇒If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the turn signal/multifunction switch.
    ⇒If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.
  4. Connect a test lamp between the headlamp switch headlamps ON signal circuit and B+.
  5. Turn the headlamp switch to the ON and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
    6. ⇒If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the turn signal/multifunction switch.
    ⇒If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.
  6. Connect a test lamp between the park lamp switch ON signal circuit and B+.
  7. Turn the headlamp switch to the PARK and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
    8. ⇒If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the turn signal/multifunction switch.
    ⇒If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.
  8. If all circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for BCM replacement, setup, and programming