Fog lights are always on, unless I turn on the headlights...

[Guest AndrewReatta]

Hello everyone. Oddly enough after a trip this fall in my 89 the fog lights now come on whenever I turn the car on, it doesn't matter if the fog light switch is on or off the lights are on. However, if I turn the headlights on the fog lights operate normally with the switch and can be turned off but as soon as the headlights are off the fog lights go back to being on constantly. I've tried swapping out the fog light relay with a new one only to have the same result. Does anyone have an ideas as to why this could suddenly happen?

[Guest Mc_Reatta]

Two ways to turn on the fog lights come to mind, the switch in the console which should also illuminate the led beside it, (is it on) or the BCM can be programmed to use them as running lights and turn them on with the ignition.

Has the BCM been replaced or played with around that time?

Does pulling the relay turn them off?

[Guest AndrewReatta]

Pulling the relay does turn them off. The BCM is the same, I haven't done anything to reprogram it or switch it out. The fog lights are on if the light next to the fog light switch is on or off, unless the headlights are on then they work normally.

How can they be set up to run as running lights? I haven't run into anything like that in the service manual but would be interested to see what the system says if you can tell me what to look for, Thanks.

[Rawja]

If the fogs are being utilized as DRLs your parking lights and taillights won't be illuminated. It's very unlikely that the option value sum has been somehow accidentally changed in the BCM.

[padgett]

Sounds more like a headlamp switch or wiring issue.

[Guest AndrewReatta]

None of the parking lights or anything else are on, they do however turn on with the fog light switch as they would normally.

I did check and saw that both codes B122 and B123 were in the history, could this have something to do with the light switch? The slider for the interior lights works normally as do the buttons to turn the headlights on and off and to turn the parking lights on and off.

Edited November 16, 2011 by AndrewReatta (see edit history)

[Barney Eaton]

Try this..........

Pull the relay, check relay across pin 1 & 4 if you have continuity, the relay is bad.

If the relay is open (good) then check pin socket #2 to see if it is grounded.

If it is grounded, then the BCM is giving it ground, the problem is then either the switch or the BCM.

This test is for a 1990, other years should be the same but I did not check schematics and you did not say what year you have.

[Guest Mc_Reatta]

Headlight switch gets a pass on this problem for an 89.

There is another player in this circuit and that's the Theft Deterrent Relay.

It can ground pin 2 of the fog light relay to turn on the lights regardless of what the BCM is doing. Normally it would flash the fog lights, the parking lights and blow the horns when the alarm has been triggered, not turn them on continuously though.

Getting to this relay under the dash to the left of the steering column is a PITA, but you could disconnect it to see if that solves the problem.

This relay doesn't affect the signal to the starter (that's the starter interrupt relay) so it could be left disconnected for a while if need be.