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Brake lights not working

Tiny
KYARBOUGH
  • MEMBER
  • 2005 CADILLAC CTS
Left & right brake lights don't work. Center light does. Bulbs and fuses check out OK, what else could be the problem? The turn signal lights are actually the yellow light below the red section of the tail lamp. They work just fine. When the driving lights are on the tail lamps light one of the two filaments. The 3rd light also works. Any other thoughts?

Thanks, Kevin
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Monday, September 29th, 2008 AT 1:58 PM

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Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
It looks like the brake lights go through the ABS controller here is the wiring diagram so you can look how the system works. The BAS relay could be out as well here is a guide to help you test the relay

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

and to check the BAS fuse 15 amp in the rear of the car

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the diagrams (Below) Please let us know what you find. We are interested to see what it is.
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Monday, September 29th, 2008 AT 4:10 PM
Tiny
KYARBOUGH
  • MEMBER
  • 4 POSTS
With the car started and the driving lights on, there is no power to the white wires that enter the light sockets.
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Monday, September 29th, 2008 AT 4:22 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Need to check with someone pressing on brake pedal. It sounds like the module is bad here is a guide to help you see what you are in for when doing the job.

https://www.2carpros.com/articles/how-to-replace-a-abs-controller

Please let us know what happens.

Cheers
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Monday, September 29th, 2008 AT 4:40 PM
Tiny
KYARBOUGH
  • MEMBER
  • 4 POSTS
Yep that was it I found the power was going in but not coming out. I got the part on Amazon for $149.99 put it on myself. Thanks for the tip I love this site.
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Monday, September 29th, 2008 AT 4:44 PM
Tiny
GMALIBU004
  • MEMBER
  • 1 POST
I have the exact same problem. Both Lights are out, but third light works? No power to the white wires did the module all good.

Many thanks
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Wednesday, May 6th, 2009 AT 8:06 PM
Tiny
FACTORYJACK
  • MECHANIC
  • 4,159 POSTS
Replace the bulbs, uppermost bulb in each lamp assembly. I believe the service # is 3057. Remove the trunk opening sill plate, pull away the side trim panels to access the 10mm nuts(2). Odds are that one was out, and eventually the other went.
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Wednesday, May 6th, 2009 AT 9:45 PM
Tiny
FACTORYJACK
  • MECHANIC
  • 4,159 POSTS
THB, is your high mount working as well? Looking at my schematic from GM service information, the white wire comes from the BAS relay and hits a splice pack(or joint connector), that is part of the rear LH fuse block under the seat cushion. From this joint connector, the three powers for the lights exit. The only possible way that both rear bulbs don't brake, but the high mount does, is if there is a fault with that joint connector, C410 for left light AND C411 right both pins b, or the individual right and left sockets. The left and high mount share ground G402, and the right uses G401. If nothing works, then yes, it could be the BCM.
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Wednesday, June 24th, 2009 AT 10:13 PM
Tiny
RONINSEC
  • MEMBER
  • 1 POST
How would I test this joint connector and where are these pins on the connector located for the test
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Wednesday, November 4th, 2009 AT 5:44 PM
Tiny
MATTMEHAFF
  • MEMBER
  • 1 POST
Okay I just had the same problem with my 2005 CTS. Side break lights not working but center brake light works good. Did a bunch of troubleshooting changed bulbs, checked fuses, checked relays. Ended up realizing there's actually 5 brake lights! Two in each back light & the one center. The first bulbs that I had changed were the center bulbs in each side tail light. They looked great but I changed them anyways. Tonight I went to change the top bulbs in each side tail lights and they both were fried. Changed them out with 3157 bulbs and everythings working good. I did notice that the bulbs I pulled out were 3057 not 3157 which is what they should've been. I'm guessing this is a factory error since I've seen about 5 other Cadillac CTS around the same year as mine with there side brake lights out and middle light good. Hopefully this helps. Long story short buy 4- 3157 bulbs and replace both top and center bulbs in each brake light compartment. Worked for me
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Wednesday, August 17th, 2016 AT 1:09 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,256 POSTS
Hey,

Great addition to this thread! Please feel free to help out on the site whenever it can add information that will help people.

Best, Ken
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Monday, February 27th, 2017 AT 10:56 AM
Tiny
FRANKGUERRERO
  • MEMBER
  • 2 POSTS
  • 2005 CADILLAC CTS
Electrical problem
2005 Cadillac CTS 6 cyl Two Wheel Drive Automatic 150k miles

My brake lights are not working, everybody else's questions like this one say their third brake light works. Mine does not, both corner lights and third (top) brake light do not work. Bulbs turn red when the lights are on, but they don't flash when i press the brakes. what could be the problem?


https://www.2carpros.com/forum/automotive_pictures/582144_DSC01048_1.jpg

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Monday, February 27th, 2017 AT 10:56 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the brake switch
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Monday, February 27th, 2017 AT 10:56 AM (Merged)
Tiny
FRANKGUERRERO
  • MEMBER
  • 2 POSTS
What if I can not find the brake switch? Do you know where its located exactly?
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Monday, February 27th, 2017 AT 10:56 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Follow the brake pedal arm till it meets up to the brake support bracket you'll find it here
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Monday, February 27th, 2017 AT 10:56 AM (Merged)
Tiny
ROBERT MOALES
  • MEMBER
  • 1 POST
  • 2005 CADILLAC CTS
Electrical problem
2005 Cadillac CTS V8 Two Wheel Drive Automatic

brakes lights not working all other lights work all fuses are good brake switch changed figured it must be a lighting problem
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Monday, February 27th, 2017 AT 10:57 AM (Merged)
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Probably faulty Electronic Brake Control Module at right front corner of engine compartment
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Monday, February 27th, 2017 AT 10:57 AM (Merged)
Tiny
FACTORYJACK
  • MECHANIC
  • 4,159 POSTS
Are all brake lamps inoperative, does the high mount lamp illuminate. This would confirm that the switch circuitry is functional. If the high mount functions, I would replace bulbs first, before going any further.
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Monday, February 27th, 2017 AT 10:57 AM (Merged)
Tiny
STEVEM147
  • MEMBER
  • 1 POST
  • 2005 CADILLAC CTS
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 48,000 MILES
Electrical problem
2005 Cadillac CTS 6 cyl Two Wheel Drive Automatic 48000 miles

Rear brake lights are not working. The middle brake light across the trunk is still working.
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Monday, February 27th, 2017 AT 10:57 AM (Merged)
Tiny
FACTORYJACK
  • MECHANIC
  • 4,159 POSTS
Since the high mount works, that verifies at least the switch is functioning. I would try a bulb in at least one side, see if that corrects it. If so, replace the other one.
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Monday, February 27th, 2017 AT 10:57 AM (Merged)
Tiny
BENHOGAN
  • MEMBER
  • 1 POST
  • 2005 CADILLAC CTS
  • 3.6L
  • 6 CYL
  • RWD
  • MANUAL
  • 150,000 MILES
All 3 brake lights are out. Changed the bulbs and the pedal position switch. Checked the BAS fuse and BAS relay. Fuse is fine, and the relay tests fine, and can be heard clicking when the brake pedal is depressed. Swapped the BAS relay with the rear defrost relay (same part number), no change. There is no + power getting to the brake bulbs. If I put + directly into the plug at the bulb I get brake lights, so the ground feed is getting there fine.
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Tuesday, April 23rd, 2019 AT 2:28 PM (Merged)

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