PRE-RELEASE
DTC B257A
| DTC B257A |
| 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 Descriptor |
DTC B257A 00
Headlamp Switch Input Signals Correlation Malfunction
| Diagnostic Fault Information |
| Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
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Headlamp Switch Input Signal
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-
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B257B 03
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B257B 07
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B257A 00
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| Circuit/System Description |
When the headlamp switch is placed in the low beam or park position, the body control module (BCM) will receive a ground signal through the headlamp switch headlamps signal circuit and the park lamp switch signal circuit.
| Conditions for Running the DTC |
The ignition is in ON, ACCESSORY or RUN position.
| Conditions for Setting the DTC |
The BCM receives an unexpected signal along either the headlamp switch OFF circuit or the headlamp ON circuit.
| Action Taken When the DTC Sets |
The BCM disregards the headlamp switch input and defaults to automatic headlamp function.
| Conditions for Clearing the DTC |
The BCM clears this code from current when the fault is removed from the system.
| Reference Information |
Schematic Reference
Exterior Lights Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Exterior 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, turn the headlamp switch in the low beam position. The low beam lamps should be ON.
Turn the headlamp switch in the OFF position. The low beam lamps should be OFF.
| Circuit/System Testing |
| 1. |
Ignition OFF, disconnect the S30 Headlamp Switch harness connector.
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| 2. |
Test for less than 5 Ω between the ground circuit terminal 6 and ground.
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| 3. |
If greater then the specified value, test the ground circuit for an open circuit/high resistance.
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| 4. |
Reconnect the S30 Headlamp Switch harness connector.
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| 5. |
Disconnect the harness connector X1 at the K9 Body Control Module.
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| 6. |
Connect a test lamp between B+ and the signal circuit terminal 22.
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| 7. |
Turn the headlamp switch between the auto and parklamp position. The test lamp should turn ON and OFF as the switch is cycled.
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| 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 S30 Headlamp Switch.
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| 9. |
If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the S30 Headlamp Switch.
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| 10. |
If all circuits test normal, replace the K9 Body Control Module.
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| Component Testing |
Static Test
| 1. |
Ignition OFF, disconnect the S30 Headlamp Switch harness connector. Turn the S30 Headlamp Switch in OFF position, test for less than 5 Ω between the terminal 6 and terminal 5.
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| 2. |
If greater than the specified value, replace the S30 Headlamp Switch.
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| 3. |
Turn the S30 Headlamp Switch in PARK position, test for less than 5 Ω between the terminal 6 and terminal 3.
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| 4. |
If greater than the specified value, replace the S30 Headlamp Switch.
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| 5. |
Turn the S30 Headlamp Switch in low beam position, test for less than 5 Ω between the terminal 6 and terminal 4.
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| 6. |
If greater than the specified value, 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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