[m2carb]

Good morning group,

Our 2013 Cruze had a problem back at Christmas time where the brake lights stayed on overnight, killing the battery. We replaced the brake positioning sensor, had it calibrated, and things were good until Wednesday night this week. Got up the next morning, same thing, battery was dead. Put the battery charger on last night and the brake lights were stuck on again! I disconnected the battery, so it could charge without the brake lights trying to drain it at the same time.

This morning, reconnected the battery and the lights are off. As these things become more and more complicated, I am sensing that what controls the brake lights is a function of the brake positioning sensor, and not the sensor itself.

Is there a relay or another module that the sensor sends a voltage to in order for the brake lights to turn on? Any help is greatly appreciated!

Thanks!

 

[_MerF_]

That's an interesting one. I don't have anything to add other than what you already suspect.

Good luck!

 

[ChevyGuy]

As I think you've figured out, the brake position sensor isn't a brake switch, it senses the position of the brake pedal. This is used by the computer to know what you're doing as well as being used by the BCM to act like a brake switch.

I'd look at a problem with the pedal itself. I'm thinking it's not always going back to the same position. I'm sure over time the computer looks for the "highest" position of the pedal and considers that "home". If the pedal doesn't return back to "home" then the brake lights will remain on. In other words, I don't think this is an electrical problem so much as it's a mechanical problem. The pedal must consistently return to the same exact position each time.

 

[m2carb]

Thanks for the responses so far, I tried to pull up on the brake pedal and there was no movement in the "up" or no brake position, however we could push down, tried that combination several times, no luck with the lights turning out, and the pedal will not go any further up. I disconnected the battery last night, even though the battery was already dead, as I did not want to charge the battery and have my charger also illuminate the brake lights at the same time. This was after I verified the brake lights were why the battery was drained, they turned on as soon as I connected up my charger to the battery.

This morning I reconnected the battery and the brake lights were off, I depressed the brake pedal several time to verify the brake lights turn on and off as expected, for now. That's why I am wondering if the power to the actual lights comes through a relay and perhaps that relay is sticking intermittently? The six terminals on the brake positioning sensor are so small I can't imagine the brake lights get the power directly through that sensor. I could be mistake but that makes the most sense to me, that there is perhaps a relay involved somewhere.

Or maybe the positioning sensor is not calibrated correctly?

 

[ChevyGuy]

The positioning sensor is actually 2 sensors (for redundancy). It's two variable resistors. So the three lines (for each sensor) are power, ground and the sensed position. All of the lines connect back to the BCM which uses the information for various things - including the brake lights. The brake lights are driven directly off the BCM. No relays.

So for some reason the BCM is deciding to turn on the brake lights. My guess is that somehow the BCM is losing it's calibration. I'd assume it's because of some kind of mechanical fault that causes the sensed home position to be unstable. There are various codes that are described if the sensed value goes outside of limits - such as you'd have with a short or open. But I suppose a bad connection could cause problems without setting a code. You might want to throw a scanner on it and see if there's any codes. (Of course disconnecting the battery has cleared them. You'll have to wait for a occurrence.)

It seems to me you've already changed the part that would be the most likely suspect. Only thing I can suggest is to look at the linkage and see if there's any slop. Changing the BCM would be rather expensive, and strikes me as unlikely.

Of course, I'm assuming there's no aftermarket stuff attached anywhere that could affect this. I'm not sure what it would be. An aftermarket cruse control? Anything plugged into the OBDII connector?

 

[m2carb]

An update, the brake linkage was sticking intermittently! Thanks to ChevyGuy for pointing at a mechanical issue rather than an electrical issue. It is amazing the amount of knowledge there is on these forums, Thanks for everyone's help!

 

[ChevyGuy]

An update, the brake linkage was sticking intermittently!

Cool! Did you find the cause of that?

 

[m2carb]

There was some corrosion causing the linkage to stick, but not all of the time, cleaning and lubrication seems to have taken care of it. Thanks again for the pointer.

 

[cgilliam1]

I know this is an old post, but where exactly is the brake linkage located ? I'm having the same problem.

 

[Dngrsone]

This would be the mechanical parts where the brake pedal attaches to the firewall and the power steering unit inside the cockpit.

 

[cgilliam1]

Thanks!! We'll give it a try.

 

[NickD]

Ha, have to correct myself in saying "always hot" is new, even the brake light, one of them on my 30 Olds was always hot, and if the pedal didn't come back by itself full up, it would stay on. By always hot being new, this is like in the last 27 years, and headlamps were always hot, had to remember to switch them off.

Can't use a simple switch anymore, the Cruze:

"Brake Pedal Position Sensor Calibration

Calibration Criteria

Note:
Do not apply the brake pedal during the brake pedal position sensor calibration procedure. Any movement of the brake pedal during this procedure will cause the calibration procedure to fail. If this occurs, the brake pedal position sensor calibration must be repeated.

Brake pedal position sensor calibration must be performed after the brake pedal position sensor or body control module (BCM) have been serviced. The calibration procedure will set the brake pedal position sensor 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 serial data.

Calibration Procedure

1. Apply the parking brake.
2. Place the transmission in the PARK position for automatic transmission or NEUTRAL position for manual transmission.
3. Install a scan tool.
4. Clear all BCM DTCs before proceeding.
5. Navigate to the Configuration/Reset Functions menu of the BCM.
6. Select the Brake Pedal Position Sensor Learn procedure and follow the directions displayed on the screen."

Brake lights this spring on my Chevy P-30 motohome chassis stayed on, simple switch, but the brake pedal was not coming up. With the brake pedal high up in the cab and that master cylinder mounted on the frame, you can only imagine the long line the linkage is. Had to clean and lubricate all of it and its only 35 years old.

Several vehicles used a brake pressure switch, fluid would leak out when replacing it, thanks Chevy for not using this with ABS, need a scanner to properly bleed the brakes. Ha, just saying it can be worse.