Brake lights #446

[David446]

Brake lights were working after build but now something has changed. Wired the rear lights that came with kit and everything worked correctly. Now brake lights stay on. I thought it was the brake light sensor because it was loosely attached to the mount and was a little damaged, so i replaced it. No change happened. Switch wires are Brown - ground Yellow - 2 volts 3 volts when brake is applied, White - 11 volts constant.
Key on, disconnect sensor, brake lights on all the time. Engine running brake lights off and don't operate when pedal applied.
After engine has been running and no brake lights, key turned off then ignition turned on brake light come on in 5 seconds.
Is there a way to go from the switch to the lights with a new wire? Why are the two wires charged (yellow and white) at all times?
Thanks for any help

 

[snirtman]

Here's the wiring description on the tail lights:

On the car's harness the black wire will be ground, yellow/green are stop/turn signal, brown is running lights.

 

[Ross]

David, What donor car did you use?
On my 2006 supercharged 2.0L Cobalt, the stop lamp switch has 12V+ on the red wire with a white stripe,
and after the brake is pressed, the light blue wire coming out of the switch goes to 12V+.

The

...
Is there a way to go from the switch to the lights with a new wire? Why are the two wires charged (yellow and white) at all times?
Thanks for any help

The brake switch wires don't go directly to the brake lights. The switch wires signal goes back into the Body Control Module (BCM), and there is some computer logic that combines the brake signal with the turn signals, and allows the rear tail lights to be both brake and turn lights, the Rear Center High Mount Light to be just a brake light, and the front mirror lights are just turn lights.

The fact that you are measuring 2, 3 and 11 volts instead of 0 and 12 volts has me thinking your car isn't getting proper power to the switch.
Either that or your donor is quite different than mine... as I don't have a brake light sensor... just a brake light switch.
I would be checking the ground wires to the BCM (near the passengers feet in our goblin) with a meter, and making sure they are 0 Volts to the battery. Or run a jumper wire from the ground post to the battery ground... see if that helps.

Also, the brake pedal in my car has a Terminate Cruise Control (TCC) switch that isn't part of the brake circuit. It has a pink wire (ignition switched 12V+) that outputs a purple wire going to the ECU.

 

[David446]

Ross, thank you for the information. I have a 2009 2.2 LT and the vehicle wiring harness is as follows with all lights working except for brake lights, which have been disconnected at peddle switch.
backup lights are green, ground is black, yellow is left turn and dark green is right, and light green is reverse.
When I connect the brake switch all the lights work but the brake light stays on constant. This makes me think the BCM is the issue. Is this the correct logic?
Thanks

 

[Ross]

Your car is quite different than mine. Hopefully someone with later donor can tell us.

 

[ATMironov]

Ross, thank you for the information. I have a 2009 2.2 LT and the vehicle wiring harness is as follows with all lights working except for brake lights, which have been disconnected at peddle switch.
backup lights are green, ground is black, yellow is left turn and dark green is right, and light green is reverse.
When I connect the brake switch all the lights work but the brake light stays on constant. This makes me think the BCM is the issue. Is this the correct logic?
Thanks

I

You should only have 5 Volts on the white wire
From my previous testing: If you power on the car with the BPPS @ 0% or 100% Loaded, the BCM sees it as a failed sensor and turns the brake lights on no mater if you change the position of the sensor. You must unplug the battery to reset.
The BCM is looking for about 1v from the BPPS to keep the brake lights off. At about 1.4v it will turn on the brake lights. If the sensor output drops below about .75v or goes above 5v the BCM sees a failure of the BPPS and turns the brake lights on until you unplug the battery.

I think if you have too much voltage on the White wire, no matter what happens the BPPS potentiometer won't output a low enough voltage to turn off the lights.

Triple check the voltage on the white wire and report back.

 

[Joebob]

Ross, thank you for the information. I have a 2009 2.2 LT and the vehicle wiring harness is as follows with all lights working except for brake lights, which have been disconnected at peddle switch.
backup lights are green, ground is black, yellow is left turn and dark green is right, and light green is reverse.
When I connect the brake switch all the lights work but the brake light stays on constant. This makes me think the BCM is the issue. Is this the correct logic?
Thanks

Try losening the screw that hold the brake light senor on the brake pedal a 1/4 turn. give the sensor just a little bit of wiggle room. I found if I tightened the sensor up completely, the brake lights would stay on. Back it off a smidge and has been good for over a year.

 

[David446]

ATMironov
I saw on YouTube Where on the Cobalt's they were grounding the BMC frame and that seemed to change things a little as in repeatably. Now it acts the same each time. So, I checked the voltage, and it changed a little, White wire was 10.4, brown and yellow was 0. So according to what you said the voltage is to high. I disconnect the battery each time I change something. After the battery is reconnected and I turn on the switch the brake lights come on and then when I apply the brake the lights go out and then in five seconds, they come on again. My thoughts are the BCM is working correctly. So now I'm totally confused as what to check.
Thanks for any help

 

[Gtstorey]

You might need to get a scanner that reads BCM/Chassis codes. That can point you in a direction.

 

[Rttoys]

Brake lights were working after build but now something has changed. Wired the rear lights that came with kit and everything worked correctly. Now brake lights stay on. I thought it was the brake light sensor because it was loosely attached to the mount and was a little damaged, so i replaced it.

on the later models. You’ll need to recalibrate the brake switch If you replace it or move it. You will need a scan tool with this capability and you’ll need to ground the wire that was going to the park brake lever. Brett had to do this, maybe he will chime in on the details.

 

[David446]

Thank you I'll try that