How to fix brake switch (not replace)

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Wes
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Thank you for this ,, you’ve described my issue almost to a T ,, on my 06 Yukon my top brake light still works but cruise and tail light brakes are not functional,, would you say I have the same issue ?
check all your fuses first, otherwise you may have a short in the tail light wiring or brake light harness or bulb socket, remove both tail lights and inspect and clean the bulb sockets and check for power with a meter if no power at the socket/s trace forward from there until you find the problem.
if the 3rd (high brake light) is working then the brake switch is good. The cruise function is finding a problem somewhere else, my guess is a fuse or wiring issue causing high or low ohm's on the circuit. If you find a blown fuse and the replacement blows again then this would also indicate a short, water intrusion, etc.
 

clandr1

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Thank you for this ,, you’ve described my issue almost to a T ,, on my 06 Yukon my top brake light still works but cruise and tail light brakes are not functional,, would you say I have the same issue ?

Did you install LED brake light bulbs? I've seen this causes the issue you describe if you don't include an inline resistor of some sort.
Additionally, does your horn work?
 
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Mark Elliott

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Did you install LED brake light bulbs? I've seen this causes the issue you describe if you don't include an inline resistor of some sort.
Additionally, does your horn work?
No LEDs and I’ll check my horn when I finish work
 

Mark Elliott

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So I checked the 2 fuses that I figure could have something to do with it ,, cruise and the stop fuses are both good ( and my horn works )
 

Mark Elliott

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So I checked the 2 fuses that I figure could have something to do with it ,, cruise and the stop fuses are both good ( and my horn works )
Just as a side note I only checked fuses at the drivers door panel ,, would there be a controlling fuse under the hood ?
 

2006Tahoe2WD

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Today my cruise control stopped working. A quick check showed no brake lights either. No dash warning lights will come on. Pulled several codes related to cruise switch, brake lights etc.

P1574 Stoplamp switch circuit
P0568 cruise control set switch circuit
P0567 cruise control resume switch circuit
P0741 Torque converter clutch Tcc system stick off (?!)

I believe You will need to clear these codes before it will work again. Mine came back after a drive, so here’s what to do about that.

In case you wondered, here's how to brake switch works on the GTM800 (my 2005 anyway): Essentially a plunger pushes down and opens 2 normally closed contacts, and closes 1 normally open contact. There is a plunger with a heavy spring inside the switch. Pressing the pedal pushes the plunger in. Mine had significant black electrical burns/tarnish at the contacts inside. Just needed cleaning and voila, cruise and brake lights work again.

You can pry the switch apart easily with a small screwdriver. Take a picture so you know how each of the 6 contacts fit. I took one out at a time and lightly sanded the black off the contacts themselves. Be careful, if the spring pops out, find it and squeezer it back in. After 15 minutes of looking for the spring, i took out all the contacts to put it with the plunger back in haha. Then i reinserted each contact. Otherwise, you will bend them. Pop the switch back together and reinstall. You can use a meter to test if you want. Two of the contacts will show continuity at rest. The last one, you will need to apply considerable force with a screwdriver and something and then it will shows continuity, and the first two will not.



Yes, you can replace this switch for $17 from the local auto big box place, and you might want to. Amazon has the OEM part for $17 also (I didn't want to buy a whatever brand, and didn't want to wait). (Putting the little clip back on is a PITA).

GM Genuine Parts D891A Brake Light Switch​


Here's some pictures for reference, and a link to a video that shows the removal/installation process of the switch itself.
This is excellent. I'm getting those codes. I might just go buy a switch but good to know you can refurbish one. I did this to my air compressor switch yesterday with success so I'm on a roll regarding switches. :)
 

2006Tahoe2WD

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This is excellent. I'm getting those codes. I might just go buy a switch but good to know you can refurbish one. I did this to my air compressor switch yesterday with success so I'm on a roll regarding switches. :)
Per Alldata diagram the brake switch signals go to one or two different modules (throttle control and power train control). This probably confuses these modules when the signal goes on/off when the brake pedal is not pressed. That's why the P codes?
 

2006Tahoe2WD

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Today my cruise control stopped working. A quick check showed no brake lights either. No dash warning lights will come on. Pulled several codes related to cruise switch, brake lights etc.

P1574 Stoplamp switch circuit
P0568 cruise control set switch circuit
P0567 cruise control resume switch circuit
P0741 Torque converter clutch Tcc system stick off (?!)

I believe You will need to clear these codes before it will work again. Mine came back after a drive, so here’s what to do about that.

In case you wondered, here's how to brake switch works on the GTM800 (my 2005 anyway): Essentially a plunger pushes down and opens 2 normally closed contacts, and closes 1 normally open contact. There is a plunger with a heavy spring inside the switch. Pressing the pedal pushes the plunger in. Mine had significant black electrical burns/tarnish at the contacts inside. Just needed cleaning and voila, cruise and brake lights work again.

You can pry the switch apart easily with a small screwdriver. Take a picture so you know how each of the 6 contacts fit. I took one out at a time and lightly sanded the black off the contacts themselves. Be careful, if the spring pops out, find it and squeezer it back in. After 15 minutes of looking for the spring, i took out all the contacts to put it with the plunger back in haha. Then i reinserted each contact. Otherwise, you will bend them. Pop the switch back together and reinstall. You can use a meter to test if you want. Two of the contacts will show continuity at rest. The last one, you will need to apply considerable force with a screwdriver and something and then it will shows continuity, and the first two will not.



Yes, you can replace this switch for $17 from the local auto big box place, and you might want to. Amazon has the OEM part for $17 also (I didn't want to buy a whatever brand, and didn't want to wait). (Putting the little clip back on is a PITA).

GM Genuine Parts D891A Brake Light Switch​


Here's some pictures for reference, and a link to a video that shows the removal/installation process of the switch itself.
I bought a new GM stop lamp switch pn 15128592 but it is sort of a mirror image of the original pn 25771554. By putting the 151 in upside down I was able to get it in and hook up but I could get the shift lever out of park. I put the old switch back in and everything worked. I started this because I got a P1574. Any ideas?
Thanks. Picture attached.

Two Brake Switches.jpg
 

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