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Fog lights just stopped working

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Old Oct 13, 2015 | 07:45 PM
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Default Fog lights just stopped working

07 gxp fog lights just stop working all I see is 1 fuse if lookin at it right is there some kind of relay maybe? I don't have power to either side looked in the owners manual it only shows that 1 fuse
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Old Oct 13, 2015 | 08:09 PM
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Man, this car isn't treating you too well lately. What did you do, run some Cumberland farms Cornahol and its punishing you? Gotta be a relay somewhere.
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Old Oct 13, 2015 | 08:28 PM
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Yea she must be mad at me for something lol
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Old Oct 13, 2015 | 08:34 PM
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Most fog lights have relays, I don't know where they are though.
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Old Oct 13, 2015 | 08:38 PM
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I looked in the underhood fuse box and didn't really see anything but that 1 fog light fuse I'll trace it out tomorrow
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Old Oct 13, 2015 | 09:35 PM
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So, This can be a little harder to diagnose. Also, I'm using Monte carlo information for your Car. When i cross checked the Traction Control the wiring was the same.


There is a 10 amp fuse. This would be the first thing i would check.


There is a PCB Relay "aka a relay on the board instead of its own relay"

From what i can tell by this schematic is, the relay is soldered to a PCB Board.
The Fog switch is a ground controlled switch for the relay on the PCB Board. From the Fog Light switch has an orange wire going into the body control module. Then the body control module will ground a Dark Green White wire that is going into the underhood fuse block. This dark green/white wire is grounded which initiates the relay which then sends power to the fog lamps.

I would start at the darkgreen/white wire that is behind the underhood fuse and ground it. If you ground it, this will jump the Body Control Module and the fog light button "aka bypassing them". Once you ground the darkgreen/white wire and the fog lights turn on, then you have a body control module issue, or the fog light button is broke.

IF this does NOT work, then the relay is burned out on the PCB Board and you'll need to replace the entire fuse box or have it repaired






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Old Oct 13, 2015 | 09:44 PM
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Good info I appreciate it I'll put this to use tomorrow I'll let u guys know what I find
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Old Oct 13, 2015 | 09:51 PM
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Also, an FYI, you can always wire up your own fix and bypass the PCB Relay entirely, if this is the case i can tell you how. Still using the stock button
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Old Oct 13, 2015 | 09:55 PM
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After looking at the wiring diagram again, If the relay is burned out, the lights will not come on BUT, the fog lamp light indicator on the instrument cluster should illuminate, Does it?
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Old Oct 13, 2015 | 10:12 PM
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Originally Posted by Sint3k
After looking at the wiring diagram again, If the relay is burned out, the lights will not come on BUT, the fog lamp light indicator on the instrument cluster should illuminate, Does it?
Yes it does, I was actually thinking about jumping them off my headlights they will just be on at all times
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Old Oct 13, 2015 | 10:38 PM
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Originally Posted by tim4daflow
Yes it does, I was actually thinking about jumping them off my headlights they will just be on at all times
Going through all that trouble you might as well keep your factory fog light button...

Ok, so that rules out an issue with the Button, but it still does not rule out an issue with the "Driver" that grounds the relay, so the above still applies. The DarkGreen/White wire still needs grounded to see if they light up.

looking forward to your response.
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Old Oct 14, 2015 | 04:31 AM
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I'll definitely try the out when I get off see what I can find
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Old Oct 14, 2015 | 08:11 AM
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Originally Posted by Sint3k
So, This can be a little harder to diagnose. Also, I'm using Monte carlo information for your Car. When i cross checked the Traction Control the wiring was the same.


There is a 10 amp fuse. This would be the first thing i would check.


There is a PCB Relay "aka a relay on the board instead of its own relay"

From what i can tell by this schematic is, the relay is soldered to a PCB Board.
The Fog switch is a ground controlled switch for the relay on the PCB Board. From the Fog Light switch has an orange wire going into the body control module. Then the body control module will ground a Dark Green White wire that is going into the underhood fuse block. This dark green/white wire is grounded which initiates the relay which then sends power to the fog lamps.

I would start at the darkgreen/white wire that is behind the underhood fuse and ground it. If you ground it, this will jump the Body Control Module and the fog light button "aka bypassing them". Once you ground the darkgreen/white wire and the fog lights turn on, then you have a body control module issue, or the fog light button is broke.

IF this does NOT work, then the relay is burned out on the PCB Board and you'll need to replace the entire fuse box or have it repaired




Great info , as always. You got mad skills with diagrams!
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Old Oct 14, 2015 | 12:40 PM
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Originally Posted by rottonj
Great info , as always. You got mad skills with diagrams!
Its actually what i do in my spare time, i diagnose mechanical and electrical gremlins for a few dealerships and local shops.

Its a fast way to make 100 for just a few minutes of work.
I also specialize in cadillacs because they have tons of eletrical issues that no one can figure out.

All my Cadillac i have bought under 1k because the owners dont wanna deal with them anymore.

I have 97,98,02 Cadillac Eldorado. All where recently under 100k miles, but my Pearl white one just went over 100k. They where actually gifts to my daughters
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Old Oct 14, 2015 | 12:50 PM
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Good job, had a 99 Eldorado that was given to me. It was really nice with 60k on it. I didn't want to deal with it either. ****** thing always had a dead battery lol.
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Old Oct 14, 2015 | 01:12 PM
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Originally Posted by rottonj
Good job, had a 99 Eldorado that was given to me. It was really nice with 60k on it. I didn't want to deal with it either. ****** thing always had a dead battery lol.


That is there biggest problem. There are many modules that will wake up and go to sleep, wake up go to sleep. So when you do an amp draw test, you may only see 30milamps , but in an hour something will turn on and draw 2amps for no telling how long, and then the cycle repeats. Most of the time its not worth replacing the module and its best to get a kill switch for the batterys.

On my red cadillac i have a 250AMP relay built into the battery that disconnects the car from a flip of a switch inside the cabin. I have this wired separate from the starter, the starter is hot at all times. I've always been concerned about having a relay that could fail and cause the entire car to shut down, but, I have yet to have any problems in 5 years. I thought about wiring up a redundant relay incase it failed but never had a need to
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Old Oct 14, 2015 | 01:24 PM
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I traced it down to a bad trunk motor that was leaving the light on. Dealer wanted 400 to replace, I fixed it for about 30 bucks. It wasted the battery though, had to replace that too. Could have been more wrong too as you say, wasn't about to waste all my time hunting gremlins.
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Old Oct 14, 2015 | 08:51 PM
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I did some tracing and found that I don't have power to the fuse box so there is something between the switch and fuse box I'll try to trace from the fuse box to the switch see what I find........and also the fog lights share the same ground as ever other light on the front of our cars so it's nothing to do with ground at all
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Old Oct 14, 2015 | 11:02 PM
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Originally Posted by tim4daflow
I did some tracing and found that I don't have power to the fuse box so there is something between the switch and fuse box I'll try to trace from the fuse box to the switch see what I find........and also the fog lights share the same ground as ever other light on the front of our cars so it's nothing to do with ground at all
The fuse will not read 12 volts unless the relay is engaged internally on the fuse box. The fuse is not hot at all times like others would be normally

So it goes like this

Switch >> Body Control Module >> Relay >> fuse >> lights
-------------------^------OR-----------^
One of those 2 is broke

So, you need to get a buddy and have them push the fog light on and off while someone listens at the fuse box, do you hear a click ?

let me know, i included a diagram below to help you.

If you do not hear any clicking, then the relay is internally damaged OR the body Control Module Driver is damaged. Or the wiring inbetween the body control module and the relay is damaged

IF you DO hear a click, and there is still no power on the fuse then the relay is damaged or the Fuse block itself is damaged internally, likely a burned tracer on the PCB Board


Last edited by Sint3k; Oct 14, 2015 at 11:13 PM.
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Old Oct 15, 2015 | 08:53 AM
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Originally Posted by tim4daflow
I did some tracing and found that I don't have power to the fuse box so there is something between the switch and fuse box I'll try to trace from the fuse box to the switch see what I find........and also the fog lights share the same ground as ever other light on the front of our cars so it's nothing to do with ground at all
I know its unlikely, but have you checked the bulbs? Mines an 08, and I have never changed them, they don't last forever. just a thought.
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