DTC B257A
Diagnostic Instructions
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
|
Headlamp Switch Input Signal
|
-
|
B257B 03
|
B257B 07
|
B257A 00
|
|
| |
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
Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
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. |
| 2. |
Disconnect the negative
terminal of the C1 Battery. |
| 3. |
Test for less than 5 Ω
between the ground circuit terminal 6 and ground. |
| ⇒ |
If greater then the specified value, test the
ground circuit for an open/high resistance. |
| 4. |
Reconnect the negative
terminal to the C1 Battery. |
| 5. |
Reconnect the S30 Headlamp
Switch harness connector. |
| 6. |
Disconnect the X1 harness
connector at the K9 Body Control Module. |
| 7. |
Connect a test lamp between B+
and the signal circuit terminal 16. |
| 8. |
Turn the headlamp switch
between the low beam and parklamps position. The test lamp should
turn ON and OFF as the switch is cycled. |
| ⇒ |
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. |
| ⇒ |
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. |
| 9. |
If all circuits test normal,
replace the K9 Body Control Module. |
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. |
| ⇒ |
If greater than the specified value, replace the
S30 Headlamp Switch. |
| 2. |
Turn the S30 Headlamp Switch
in PARK position, test for less than 5 Ω between the terminal
6 and terminal 3. |
| ⇒ |
If greater than the specified value, replace the
S30 Headlamp Switch. |
| 3. |
Turn the S30 Headlamp Switch
in low beam position, test for less than 5 Ω between the
terminal 6 and terminal 4. |
| ⇒ |
If greater than the specified value, replace the
S30 Headlamp Switch. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|
