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wrench9124, ASE Certified Technician
Category: Car
Satisfied Customers: 3432
Experience:  GM Master Certified, ASE Master Certified, 32 years exp, GM Hybrid Certified, GM Mark of Excellence
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Pontiac G6: Rear brake lights work the reverse..malfunction..dashboard

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My Pontiac G6 has the same brake light problem as in other web posts: Rear brake lights work the reverse of how they should. No sign of malfunction on dashboard. While key is on, brake lights are on. When pedal is pressed brake lights go out. I don't have schematics so can't see if a brake relay shorted/grounded terminal could be the cause. Other web posts suggest the (expensive) Body Control Module is the problem, but I have found no confirmations. One web post said the problem occurred after replacing brakes (could have happened, I didn't notice when mine were replaced); if so, then I assume some sensor is calibrated after the dealership replaces brakes (mine weren't replaced by a dealer).
Hello, and welcome. you are thinking right here. the brake lights on turned on by the Body control module. the BCM receives a class two signal from a brake position sensor mounted on the brake pedal. and yes this brake position sensor has to calibrated with GM tech scan tool!!! along with the wiring diagram, do you need a detail function description on how the lights work??
Customer: replied 8 years ago.

Yes, along with the wiring diagram, a detailed functional description would be fantastic, better than the source code! A flow chart would work just as well, too.


The brake petal height is adjustable by a control next to the steering wheel (I've never tried it). If the pedal height has to be adjusted after brake pad replacement, I would expect the mechanic to use this adjustment and not monkey with anything else around the pedal. I assume the pedal height control is designed to allow pedal adjustment without throwing calibration around the pedal out of whack. So I would think the only thing that needs calibration is near the brake actuators at the wheel, or maybe in the ABS module. Is there something to adjust at either location?

The only adjustment, is what is called a brake sensor recalibrate. this is only usually done after the switch has been replaced or some sort of reprogramming has been done. here is the wiring diagram, and how the system works along with the calibration. but keep in mind, the ONLY WAY, this can be ajusted or reclaibrated is with a GM TECH SCAN tool.


If there is anything else I can answer, please feel free to ask!!!



Object Number:(NNN) NNN-NNNN Size: FS



The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery positive voltage to the stop lamps, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil side. When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the STOP LP fuse to illuminate the center high mounted stop lamp (CHMSL).


The brake pedal position sensor (BPPS) receives a low reference signal and a 5-volt reference signal from the BCM. Whenever the brake pedal is applied, the BPPS applies a variable voltage signal to the BCM through the stop lamp switch signal circuit. The BPPS calibration must be performed after the BPPS or body control module (BCM) have been serviced. The calibration procedure will set BPPS home value. This value is used by the BCM to determine the action of the driver applying the brake system and to provide this information to the vehicle subsystems via the class 2 communication bus.

Brake Pedal Position Sensor Calibration

  1. Install a scan tool.
  2. Select Diagnostics.
  3. Turn ON the ignition, with the engine OFF.
  4. Select the vehicle.
  5. Select Body and Accessories.
  6. Select Lighting Systems.
  7. Select Module Setup.
  8. Select BCM.
  9. Select the BPPS calibration procedure and follow the directions displayed on the screen.


wrench9124 and 2 other Car Specialists are ready to help you
Customer: replied 8 years ago.

Thanks. Sounds like I will have to take the car in to get the brake pedal position sensor calibrated.


I'm tempted to make the adjustment myself, experimenting until the lights come on at the right pedal movement. Considering the current behavior of the brake lights, I don't have anything to lose.

yes, that would be your next step, especially if the sensor has been moved.


I hope I have been helpfull, and if you have any other questions, Please feel free to ask!!

Customer: replied 8 years ago.
Where is the Brake Pedal Position Sensor? You have a picture?

sure, here is a picture.


Above Brake Pedal

Object Number:(NNN) NNN-NNNN Size: MF

(1)Brake Pedal Position Sensor
(2)Adjustable Pedals Position Sensor


Object Number:(NNN) NNN-NNNN Size: SH