B3903
DTC B3903
Circuit Description
The body control module (BCM) supplies voltage to the center high mount stop lamp (CHMSL) and the powertrain control module (PCM) when the stop lamps are active.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B3903 Stop Lamp Relay Circuit
Conditions for Running the DTC
* The BCM must be powered.
* This test is run continuously.
Conditions for Setting the DTC
B3903.02
Will set if the stop lamp switch signal circuit is shorted to ground for 125 ms.
B3903.05
Will set if the stop lamp switch signal circuit is open or shorted to voltage for 125 ms.
Action Taken When the DTC Sets
* When DTC B3903 is set the service vehicle soon lamp will illuminate.
* The CHMSL output is disabled.
Conditions for Clearing the DTC
* The current DTC will clear when the fault is no longer present.
* The ignition key must be cycled OFF and ON.
* A history DTC clears after 100 consecutive ignition cycles in which no faults have occurred.
* Clear the DTC with a scan tool.
Diagnostic Aids
* An internal short in the CHMSL may cause this code to set.
* A faulty brake lamp diagnostic resistor may cause B3903.05 to set.
Test
