Brake Lights

[Red27]

Ok so here's the problem while driving the car the lights turn on all around, but when braking only the third brake light turns on. all the signals work so I know the bulbs are good.

Does anybody have a clue as to why this is happening or possibly an innovative solution that I haven't thought of yet?

Oh and just in case it's important the car is an auto 07 LT

seriously though I'm stumped here

[white balt]

Okay, so what have you checked already?

Fuses or anything?

BTW, do they turn off when you hit the brake?
Or do they just not get brighter?

[Insert signature here]

[Coby7]

To start off, there is only one brake switch, this switch supplies a ground to both (high brake light and brake bulbs on either side of your Cobalt) this same switch with the same contact also disactivates cruise if it's on. So you know it's not your brake switch.

2. High brake light has battery B+ which differs from tail brake light which has ignition 1 B+.

3. Brake lamp fuse refers to tail brake lights and not high brake lights.

For rear tail brake lights to work ignition has to be on, (with a good fuse) while high brake lights come on as soon as you touch the brake pedal.

My theory here is, You assumed your brake fuse was good because you have high brake lights working. I would check brake fuse #9 (10 amp) on BCM fuse block in passenger side center console . This is your most likely cause.


High brake light fuse is same as trunk courtesy lamp and rear window defog I believe.

[ChevyCustSvc]

I hope you've had some luck checking into the fuses; if you were to decide upon bring your Cobalt to your dealership, or would like for me to check for any open recalls/provide warranty information, please send me a private message that includes the last 8 of your VIN and we'll go from there.

Best,
Sarah
GM Customer Service

[Red27]

Ok so I checked the fuses and they are good. And fuse 9 in the passenger side controls the high mount stop light. What I did was test the wires going to the brake lights to see if there was any current going to then when the brakes are applied but no dice. Although from what I'm reading I think I should have been looking for ground instead. Is that right?

[Coby7]

I will try and download the brake schematic...

---------- Post added at 09:43 PM ---------- Previous post was at 09:25 PM ----------

But until I find it heres what I found on 2007 stop lamp.Stop Lamps....
The body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the brake pedal position sensor. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The stop lamps are grounded at G401 and G403. The CHMSL is grounded at G302.

---------- Post added at 09:47 PM ---------- Previous post was at 09:43 PM ----------

Do your 4way flashers work in the back?

---------- Post added at 09:47 PM ---------- Previous post was at 09:47 PM ----------

Do you have OEM bulbs?[COLOR="Silver"]

---------- Post added at 10:07 PM ---------- Previous post was at 09:47 PM ----------


OK, this might also be my mistake, there is only one brake switch but it has 2 wires on one of the terminals. If you hear the shifter solenoid when you press the brake pedal this means BCM is getting the brake pedal signal therefore no broken wires at switch . So problem has to be BCM if you have 4way flashers. Anyway here's the diagram. If you need any help understanding the diagram feel free to ask.

[Red27]

The 4 ways flash, but when braking the lights don't brighten up. As for the schematic I can follow the basics of out I'm just unsure of what it's telling me. But now I see that I need to look for the bcm and see what I can find wrong there

[Coby7]

It is the same wiring for Brake lights as for 4 way flashers. So your wiring is good. Looks like you might need a visit @ a garage with a Tech 2 because I think your BCM has shit the bed. But to make sure you can check pins "A9 and A12" of C3 of the BCM to see if you have voltage when applying brake with ignition on.

---------- Post added at 11:52 PM ---------- Previous post was at 11:51 PM ----------

Are your 4way flashers bright?

[Red27]

The flashers seem to be normal to me. with the parking lights on and the 4 ways on you see both filaments burning. Not really sure if theres more to it than that. while I get the basics of the schematic, I don't see where the bcm is located. Could you possibly point me towards it's location?

[Coby7]

You mean on the diagram or in the car?