DTC B257B
Diagnostic Instructions
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
|
|
| |
Circuit/System Description
The body control module (BCM) supplies a reference voltage to
the backlight dimmer switch, which is part of the headlamp switch.
When the backlight dimmer switch is placed in a desired brightness
position, reference voltage is applied through the backlight 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
Schematic Reference
Interior Lights Dimming Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Interior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
Circuit/System Verification
Ignition ON, switch ON exterior lighting, 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
| 1. |
Ignition OFF, disconnect the
harness connector at the S30 Headlamp Switch. |
| 2. |
Ignition ON, test for B+
between the 12 V reference circuit terminal 1 and ground.
|
| ⇒ |
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. |
| 3. |
Ignition ON, test for less
than 0.3 V between dimming signal circuit terminal 12 and
ground. |
| ⇒ |
If greater than the specified range, test the
dimming signal circuit terminal 12 for a short to voltage. If the
circuit tests normal, replace the K9 Body Control Module. |
| 4. |
Reconnect the harness
connector at the S30 Headlamp Switch. |
| 5. |
Dim the interior backlighting
with the S30 Headlamp Switch. |
| 6. |
Disconnect the harness
connector at the S30 Headlamp Switch. |
| 7. |
Install a 3 A fused jumper
wire between the signal circuit terminal 12 and the voltage
reference circuit terminal 1. 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 Body
Control Module. |
| 8. |
If all circuits test normal,
replace the S30 Headlamp Switch. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
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