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Take a look at the wiring diagram below. The important clue is you said the middle brake light isn't working.

The CHMSL (Center High Mounted Stop Light) works only from closing the dedicated relay. This signal provides power to the lamp, and also instructs the engine and transmission control modules that you are braking.

Unfortunately, this function is provided solely from the BCM (Body Control Module). If that module is bad, it can affect many things - including the CHMSL and the passenger side signals.

If the module is indeed bad, it will be an expensive repair - and involve a special "Tech" GM tool to program your vehicle's specific information.

Alephzero's comment is a good one; I would check the shared ground paths (you can see them as dotted lines in the diagram). However, I doubt the FRONT and the rear share the same ground path, which leads me back to a BCM issue.

Identify the CHMSL relay in the underhood fuse block, and have someone feel it while you pump the brakes with the car on (not running). It should click everytime you hit the brakes. If not, that's bad news and points to a bad BCM.

Good luck.

enter image description here

Take a look at the wiring diagram below. The important clue is you said the middle brake light isn't working.

The CHMSL (Center High Mounted Stop Light) works only from closing the dedicated relay. This signal provides power to the lamp, and also instructs the engine and transmission control modules that you are braking.

Unfortunately, this function is provided solely from the BCM (Body Control Module). If that module is bad, it can affect many things - including the CHMSL and the passenger side signals.

If the module is indeed bad, it will be an expensive repair - and involve a special "Tech" GM tool to program your vehicle's specific information.

Alephzero's comment is a good one; I would check the shared ground paths (you can see them as dotted lines in the diagram). However, I doubt the FRONT and the rear share the same ground path, which leads me back to a BCM issue.

Good luck.

enter image description here

Take a look at the wiring diagram below. The important clue is you said the middle brake light isn't working.

The CHMSL (Center High Mounted Stop Light) works only from closing the dedicated relay. This signal provides power to the lamp, and also instructs the engine and transmission control modules that you are braking.

Unfortunately, this function is provided solely from the BCM (Body Control Module). If that module is bad, it can affect many things - including the CHMSL and the passenger side signals.

If the module is indeed bad, it will be an expensive repair - and involve a special "Tech" GM tool to program your vehicle's specific information.

Alephzero's comment is a good one; I would check the shared ground paths (you can see them as dotted lines in the diagram). However, I doubt the FRONT and the rear share the same ground path, which leads me back to a BCM issue.

Identify the CHMSL relay in the underhood fuse block, and have someone feel it while you pump the brakes with the car on (not running). It should click everytime you hit the brakes. If not, that's bad news and points to a bad BCM.

Good luck.

enter image description here

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source | link

Take a look at the wiring diagram below. The important clue is you said the middle brake light isn't working.

The CHMSL (Center High Mounted Stop Light) works only from closing the dedicated relay. This signal provides power to the lamp, and also instructs the engine and transmission control modules that you are braking.

Unfortunately, this function is provided solely from the BCM (Body Control Module). If that module is bad, it can affect many things - including the CHMSL and the passenger side signals.

If the module is indeed bad, it will be an expensive repair - and involve a special "Tech" GM tool to program your vehicle's specific information.

Alephzero's comment is a good one; I would check the shared ground paths (you can see them as dotted lines in the diagram). However, I doubt the FRONT and the rear share the same ground path, which leads me back to a BCM issue.

Good luck.

enter image description here