Calling GM service techs; I have a good one...

[CountryBoy19]

**********SOLVED**********


I'm cross-posting this from my post on Cadillac Owners forum...

2004 Cadillac CTS rear corner brake-lights aren't working, center one is... seems to be a common issue that has no solutions that I can find online...

I'm having the same problem as in this thread: 2005 CTS Brake lights don't work

Center brake light on trunk works fine. Left & right corner brake lights do not work.

Checked the bulbs, they are the correct bulbs and they are good bulbs (verified on an ohm meter to be extra certain). No power to those receptacles for the brakes (tail-lights work fine).

BAS fuse and BAS relay under LR seat are both good.

BPP (Brake Pedal Position) was replaced 2 years ago and has worked fine since then but I checked it anyways. It seems to be working ok and I'm getting 5V out of the plug that connects to the BPP sensor. Is 5V correct considering this is a micro-electronic circuit?

What else could be the problem? Is there a solution to the problem in that thread? It seems there was never an agreed solution. The same question (have you checked the BAS relay and BAS fuse?) just kept getting repeated with no solutions beyond that... I'm stumped.​

 

[GodFearinGunTotin]

Well crap...I can't see the schematics on my Ipad. Apparently, they're only viewable on a real computer.

 

[wolfman]

Turn signals work?

 

[long coat]

On truck we have messed with at work, the turn signal switch goes bad & will cause the lights to not work. It could be the turns or brakes that quit first, but they will all stop after awhile.

 

[CountryBoy19]

Turn signals work?

Yes

Turn signals are isolated from Brake lights on the CTS. I.E. completely different bulb & wire for the turn signals.

 

[CountryBoy19]

Found a schematic for '03 Seville here: Brake Lights won't work - General Cadillac Forums - CaddyInfo Cadillac Forum

I suspect it is the same wiring harness on the CTS.

 

[cbop]

Well, looking at the schematic, if the center high mounted stop lamp (chmsl) works, all of the switching portion is good. The l brake lamp and the right brake lamp do not share any connector or ground so I would check to see what is going on at the LR fuse block joint connector terminals S24 & S25

 

[CountryBoy19]

Solved.... I'm rather ashamed to admit this but bone-headed things happen to me frequently so I'm going to save somebody else the trouble... cbop's schematic led me down the path of trying to see if I had coincidentally had 2 wires break or lose connection. It was at that point that I realized the light-bases I was looking at didn't have anything connected to the 3rd wire. It goes into the mating plug just inside the trunk and there is no wire connected to it at the other side of that plug. Doh...

The first, and most obvious "double-filament bulb" in the tail-light assembly is NOT the brake-light bulb. The 2nd filament in that bulb is "wasted" and isn't even connected to a wire, of course it isn't going to light-up when you hit the brakes. The bulb you're looking for is the highest one, the one that won't come out easy and you didn't want to risk breaking since it wasn't relevant to the failure you're trouble-shooting. I have news for you, it is very relevant...

If you couldn't figure it out, the CTS has 2 lamp bases that use the exact same bulb, one of them only lights a single filament and the other is the brake-light. The brake-light bases were very hard to get out of the assembly so I didn't want to risk breaking them when I had already found what I thought to be the brake-light bulbs (any reasonable person would assume a double-filament bulb is the brake-light or a turn-signal). Guess I learned my lesson there...