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. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Exterior Lights Schematics Connector End View Reference: Master Electrical Component List | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 |
Is the DTC retrieved as a current DTC? | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections |
3 | Is DTC B3903.02 set? | Go to Step 5 | Go to Step 4 |
4 |
Is the CHMSL illuminated? | Go to Step 6 | Go to Step 7 |
5 | Test the stop lamp supply voltage circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 10 | Go to Step 8 |
6 | Test both stop lamp supply voltage circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 10 | Go to Step 8 |
7 | Test both stop lamp supply voltage circuits for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 10 | Go to Step 8 |
8 | Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 10 | Go to Step 9 |
9 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 10 | -- |
10 |
Does the DTC reset? | Go to Step 2 | System OK |
