Circuit Description
The electronic brake control module (EBCM) sources 5 volts on the stop lamp switch signal circuit when the stop lamp switch is inactive. The voltage is supplied a ground path through the stop lamp bulbs.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C1291 Open Brake Lamp Switch Contacts During Deceleration
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The stop lamp switch input voltage is between 2.2 volts and 5.0 volts for 2 seconds.
Action Taken When the DTC Sets
| • | The EBCM disables the TCS for the duration of the ignition cycle. |
| • | The Traction Off indicator turns ON. |
| • | The message center displays the Service Traction System message. |
| • | The ABS remains functional. |
Conditions for Clearing the DTC
| • | The condition for the DTC is no longer present and the DTC is cleared with a scan tool. |
| • | The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
Possible causes of this DTC are the following conditions:
| • | A signal circuit of the stop lamp switch is open. |
| • | The stop lamp switch is misadjusted. |
| • | Verify proper stop lamp switch operation using the data list of the scan tool. As the brake is applied, the data list displays the stop lamp switch ON within 2.54 cm (1 in) of travel. |
| • | All brake lamps are open. |
| • | All brake lamp grounds are open. |
| • | Circuit has a wiring problem, terminal corrosion, or poor connections. |
| • | Loose or corroded EBCM ground or ECM ground. |
| • | An internal EBCM problem. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Tests the circuit for a change in states.
-
Tests for proper operation of the circuit by bypassing the stop lamp switch. If the fuse in the jumper opens when you perform this test, the signal circuit of the stop lamp switch is shorted to ground.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Antilock Brake System Connector End Views or Lighting Systems Connector End Views in Lighting Systems | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 | Press the brake pedal. Do the brake lamps turn ON? | Go to Step 3 | Go to Step 7 |
Does the Brake Switch Status parameter change state? | Go to Diagnostic Aids | Go to Step 4 | |
4 |
Did you find and correct the condition? | Go to Step 14 | Go to Step 5 |
Does the scan tool display Applied? | Go to Step 11 | Go to Step 6 | |
6 | Test the signal circuit of the stop lamp switch for an open between the splice pack of the stop lamp signal circuit and the electronic brake control module (EBCM). Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
7 | Test the battery positive voltage circuit of the stop lamp switch for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 8 |
8 | Test the signal circuit of the stop lamp switch for an open between the stop lamp switch and the splice of the stop lamp signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 9 |
9 | Test the signal circuit of the stop lamp switch for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 10 |
10 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 12 |
11 | Inspect for poor connections at the harness connector of the stop lamp switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 13 |
12 | Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the repair? | Go to Step 14 | -- |
13 | Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Lighting Systems. Did you complete the repair? | Go to Step 14 | -- |
14 |
Does the DTC reset? | Go to Step 2 | System OK |
