Fog Lights Not Working
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From: Rye Brook, NY
Fog Lights Not Working
My fog lights do not work, but they did go on yesterday intermittently. So the bulbs work. I checked the one fuse and its ok. The power switch is lit up as well. Any ideas where I should look? What could be the cause of the problem? Thanks
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
First thing I'd do is pull the switch and make sure the connectors are on tight at the back. The length of the wires is quite short. Its possible for them to work loose.
If both are either on or off its more likely to be at the switch end than the lamp end.
I can E Mail a wiring diagram if it helps.
If both are either on or off its more likely to be at the switch end than the lamp end.
I can E Mail a wiring diagram if it helps.
Drifting
Joined: May 2000
Posts: 1,917
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From: Southern NH
If the problem is intermittent, it's likely either the fog relay - #39 in the underhood fuse panel, or the ground G102 (and SP100).
One way to confirm the relay is to switch the #39 fog relay temporarily with #36 Horn Relay (both in the underhood panel near the battery). Both these relays should be the same, so if after the swap the fogs work and the horn is intermittent then you've found the problem.
Just to confirm, you say the power switch is lit up. Is the small indicator light on the switch lit up when the problem occurs? It gets power from the same relay circuit that feeds the fog bulbs. If the indicator is lit when the problem occurs, then the issue is with the ground for the bulbs. There's a ground splice connector on the passenger frame rail below the coolant reservoir. The splice pack connects to the ground G102 on the frame rail. Those splice packs are known to get corroded and can result in the problem you're seeing (check the sticky post at the top of the section on electrical issues). You can clean the connector pins to solve that issue.
The other candidates are the fuses, but unlikely since it's intermittent. Fuse 32 in the passenger footwell panel provides power to the switch contacts, and fuse 6 in the underhood panel provides power to the fogs and the indicator light in the switch. The BCM controls the relay, so if all the relays and fuses check out, there might be an issue in the BCM related to the fog circuits (but unlikely).
Let us know which one it was.
One way to confirm the relay is to switch the #39 fog relay temporarily with #36 Horn Relay (both in the underhood panel near the battery). Both these relays should be the same, so if after the swap the fogs work and the horn is intermittent then you've found the problem.
Just to confirm, you say the power switch is lit up. Is the small indicator light on the switch lit up when the problem occurs? It gets power from the same relay circuit that feeds the fog bulbs. If the indicator is lit when the problem occurs, then the issue is with the ground for the bulbs. There's a ground splice connector on the passenger frame rail below the coolant reservoir. The splice pack connects to the ground G102 on the frame rail. Those splice packs are known to get corroded and can result in the problem you're seeing (check the sticky post at the top of the section on electrical issues). You can clean the connector pins to solve that issue.
The other candidates are the fuses, but unlikely since it's intermittent. Fuse 32 in the passenger footwell panel provides power to the switch contacts, and fuse 6 in the underhood panel provides power to the fogs and the indicator light in the switch. The BCM controls the relay, so if all the relays and fuses check out, there might be an issue in the BCM related to the fog circuits (but unlikely).
Let us know which one it was.
Last edited by JC in XTC5; Aug 22, 2006 at 12:10 AM.
Thread Starter
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Joined: Sep 2002
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From: Rye Brook, NY
Originally Posted by JC in XTC5
If the problem is intermittent, it's likely either the fog relay - #39 in the underhood fuse panel, or the ground G102 (and SP100).
One way to confirm the relay is to switch the #39 fog relay temporarily with #36 Horn Relay (both in the underhood panel near the battery). Both these relays should be the same, so if after the swap the fogs work and the horn is intermittent then you've found the problem.
Just to confirm, you say the power switch is lit up. Is the small indicator light on the switch lit up when the problem occurs? It gets power from the same relay circuit that feeds the fog bulbs. If the indicator is lit when the problem occurs, then the issue is with the ground for the bulbs. There's a ground splice connector on the passenger frame rail below the coolant reservoir. The splice pack connects to the ground G102 on the frame rail. Those splice packs are known to get corroded and can result in the problem you're seeing (check the sticky post at the top of the section on electrical issues). You can clean the connector pins to solve that issue.
The other candidates are the fuses, but unlikely since it's intermittent. Fuse 32 in the passenger footwell panel provides power to the switch contacts, and fuse 6 in the underhood panel provides power to the fogs and the indicator light in the switch. The BCM controls the relay, so if all the relays and fuses check out, there might be an issue in the BCM related to the fog circuits (but unlikely).
Let us know which one it was.
One way to confirm the relay is to switch the #39 fog relay temporarily with #36 Horn Relay (both in the underhood panel near the battery). Both these relays should be the same, so if after the swap the fogs work and the horn is intermittent then you've found the problem.
Just to confirm, you say the power switch is lit up. Is the small indicator light on the switch lit up when the problem occurs? It gets power from the same relay circuit that feeds the fog bulbs. If the indicator is lit when the problem occurs, then the issue is with the ground for the bulbs. There's a ground splice connector on the passenger frame rail below the coolant reservoir. The splice pack connects to the ground G102 on the frame rail. Those splice packs are known to get corroded and can result in the problem you're seeing (check the sticky post at the top of the section on electrical issues). You can clean the connector pins to solve that issue.
The other candidates are the fuses, but unlikely since it's intermittent. Fuse 32 in the passenger footwell panel provides power to the switch contacts, and fuse 6 in the underhood panel provides power to the fogs and the indicator light in the switch. The BCM controls the relay, so if all the relays and fuses check out, there might be an issue in the BCM related to the fog circuits (but unlikely).
Let us know which one it was.
