Diagnosis And Testing - Stop Lamp Switch
To avoid serious or fatal injury on vehicles equipped with airbags, disable the Supplemental Restraint System (SRS) before attempting any steering wheel, steering column, airbag, Occupant Classification System (OCS), seat belt tensioner, impact sensor or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the SRS. Failure to follow these instructions may result in accidental airbag deployment.
| CONNECTOR PINOUT | |
|---|---|
| 1 | BRAKE SIGNAL 1 |
| 2 | BRAKE SIGNAL 2 |
| 3 | IGNITION RUN/START CONTROL OUTPUT |
| 4 | FUSED B(+) |
Using an ohmmeter, perform the continuity tests at the terminal pins in the brake lamp switch connector receptacle as shown in the Brake Lamp Switch Tests table below.
| BRAKE LAMP SWITCH TESTS | |
|---|---|
| PLUNGER POSITION | CONTINUITY BETWEEN |
| Released (Extended) | Pins 1 and 4 |
| Compressed (Depressed) | Pins 2 and 3 |
The brake lamp switch as well as the hard wired inputs and outputs of the switch may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, the switch can only be tested while installed and, while in the installed position, the switch terminals are inaccessible to test meter probes. The most reliable, efficient and accurate means to diagnose the electronic controls and communication related to brake lamp switch operation requires the use of a diagnostic scan tool to read the switch status through the BCM and the PCM.
- Using a scan tool, check for Diagnostic Trouble Codes (DTCs) in the BCM and PCM. If no DTCs are found, go to Step 2. If any DTCs are found, review appropriate diagnostic information to locate the DTC and repair as needed.
- Monitor the Brake Lamp Switch operation by using the diagnostic scan tool to verify that both switch states in the BCM changes while actuating the brake pedal. If actuation is detected in the BCM, move to the PCM to confirm actuation is detected.
- If damage to the switch is present for any reason the switch is to be replaced. If a switch is removed and the plunger length differs from a new switch, the switch should always be replaced and not reinstalled. The nominal height for a new switch (tip of the plunger to the body of the switch) is 16.90mm.
- 1 - Defective brake switch due to the switch tab being sheared off.
- 2 - Defective brake switch due to the switch tab being offset.
- 3 - Normal operational brake lamp switch to be used for installation.