I posted about this a while back. but the problem continues so I'm looking for some more info.

sometimes when turning the headlights on in my C5 only my driver's side headlight door opens. the passenger's side lights come on but the door stays shut. cycling the lights on and off a couple times does nothing.

if I open the hood and turn the adjuster just enough to get the door to move then all is fine. turn the lights off and it pulls closed. turn them on and it opens fully and will work from there on out for a few days until the problem reoccurres.

I have 55W HIDs in the car and a load resistor. I do not think this is related. I've had the HIDs for a couple years and this is a new problem. its always the passenger's side headlight door. I already have brass gears in it. could it be something mechanical binding? I haven't been able to dig into the headlight yet but the next thing I'm going to try is to grease the moving parts.

the setting of the high beams doesn't seem to affect it at all either. with HIDs if there is no load adjustment I know that pulling the high beams on can get the doors to close properly. doesn't seem to be the case here. plus they always close, its just one side that doesn't want to open.

when it sticks nothing electrical seems to fix. but turning the adjuster just a small mount takes care of it which makes me think its something mechanical. unless something odd could be happening making the headlight door control module act up?

 

Take a look at that particular cover with the lights down and the hood shut. See what the margin around it looks like........I had to make a small adjustment a few years ago on my drivers cover.........

 

good point, maybe the door cover itself is interfering somewhere? I'll take a look at that.

 

ok the situation here just changed. and not for the better. today I wanted to check to see how the issue was doing. I turned the lights on and neither door opened! both headlights came on just fine, but the doors didn't open at all. since I had the car off this time and the hood up I could hear a clunking sound when I flipped the switch. it sounded normal, just like the sound the motor/gears make when the headlights hit the stops at the full open or full closed position. I went up to the lights with the switch on, turned each manual adjuster about 1/4 turn in the open direction (so the doors didn't move one bit, it takes a couple turns before they even start to move) turned the switch off, both adjusters spun a little. flipped them back on, both doors opened perfectly.

I can't believe I'm the first person to have this problem, any other ideas? the covers on both sides are clear and not contacting anything when they open. so that is not the issue.

 

bump Like to see someone answer this one

 

My passenger light does the same thing. Both gears have been replaced. Check the stops to see if they are still correct, I read that in a past post. Another post made the recommendation to trace back the headlight connectors for voltage and trace back from the connector, maybe a grounding issue. Good luck, I'll be doing troubleshooting tomorrow also!

 

Sounds light the headlight motor relay finally took a crap. It's underneath the passenger side headlight. Easy fix

 

no good. just tried it, still not working right. its back to just the passenger's light now however.

I'm familiar with the headlight door control module, should be easy to replace. is there a better way to diagnose it though? I don't want to act like a dealer and just throw expensive parts at the problem until it goes away.

I just turned the lights back off when it didn't open. rotated the manual adjuster in the opening position literally 1/2 turn (so basically I just made it so that it wasn't tightly closed, the doors didn't budge one bit with that little amount of rotation) and then turned the lights back on and they both opened perfectly.

is this a normal way that the relay pack fails? seems as long as I turn the headlights on at least once a day they are fine. its only if it sits for a few days when I go to turn them on again is when I'm having the problem.

 

I had the same issue but it was on the drivers side. My headlight control module was at fault. I don't know of any way to check if it's good besides looking to see if it's melted, or cracking it open to see if anything is burnt. I thought my issues was the motor but it was gtg so then I traced it to the module. I had a schematic of everything if you know how to use a multimeter you can chase it down to the component. I don't have it anymore but I have seen it a few times posted around here.

 

this is frustrating me but getting anxious about it isn't going to help. I just want my C5 to be perfect. I know its 11 years old and has 105k on the clock now, but I still want it to operate like its brand new.

this weekend I'm going to dig into this more. part of me hopes that it is just the control module because that will be the easiest fix even though I'd have to buy a part to fix the problem. I suspect that may be the culprit so I'm going to remove and inspect it this weekend. I'll look for burn signs or other evidence of broken seals/water intrusion. how well sealed is this module? can it be disassembled to inspect it?

one piece of evidence suggesting the module is water. I haven't been paying complete attention to it so I don't know for sure. but we've gotten a lot of rain here lately. my C5 is a daily driver so its not one of the vettes that melts when wet. I know the problem does not occur all the time. it usually has to go a couple days without using the headlights before the problem occurs. its entirely possible that it only happens after its rained. the one time that the problem got worse, both doors failed to open, was right after I washed the car. I wonder if water could be getting into the module, I know they act up when that happens. maybe just drying it out and re-sealing it with silicone would fix it?

based on observation I think I know exactly what's happening when the doors fail to open. the way the module works according to the service manual is it powers the motors to open or close the headlights and monitors the current draw. when the motors reach the end of their travel they attempt to keep rotating and thus draw more and more current. the control module recognizes this as the doors having reached their full open or closed state, and kills the power. or of course there's a timeout in the event that never happens so they don't just keep running forever. when the doors fail to open I hear the motor make the familiar clunking sound which is normal. it makes that sound when the motors stop rotating in the full up or down state, its normal. whether its the sound of the motor itself recoiling slightly from the relieved strain or the sound of the relay clicking off I'm not sure. but either way, the headlights make that sound when they fail to open.

so it looks like the control module is attempting to open the headlight door, but even without the door moving the module is seeing a current draw high enough that it thinks the door has already reached its fully open state, so its immediately kills power to the motor even though it hasn't opened yet. the motors are designed to "jam" themselves somewhat in the open and closed positions. usually they have no problem whatsoever unjamming themselves from the present position in order to move towards the next desired position then the jamming effect causes the control module to know the doors are fully opened or closed. when this failure occurs it seems as if the power required to "unjam" the mechanism from its present state its too high and its causing the control module to think the headlight is closed. its the same behavior as if you manually raised one headlight to the full open state then flipped the headlights on. the module attempts to open the doors but almost immediately encounters the high current draw "im already open" condition and the doors stop trying to open.

what could cause something like that to happen? I suspect one of 3 things: it really is mechanical, something in the door opening mechanism is jamming requiring too much torque from the motor to get it moving. Or the motor is going bad. one common symptom of a motor failing could be abnormally high current draw. there's too much mechanical resistance or electrical resistance in the motor and in order to apply enough torque to "unjam" the mechanism from the closed state the motor requires enough current to trigger the control module to think its already open. Or, the module is bad causing it to mistake the situation for the doors being open already, maybe its not providing enough voltage to the motor? who knows.

if the headlight is stuck and won't open, I can turn the manual adjuster just a small amount and then it will open fine. as if I can break it loose from its closed state and then it can handle the rest of the opening process on its own. but once this is done the headlights work fine for a while, even if it needs help to unjam from the closed state once that's done it has no problem unjamming itself from the open state to reclose, or from the closed state to reopen after that's done. this kind of supports a mechanical problem to me. if the motor were bad or the control module were bad wouldn't you think it likely that the failure would happen repeatedly and not only after sitting closed for a couple of days without being opened?

there's also the factor of the driver's side light doing the same thing, just that one time. that suggests the culprit is something in common. not impossible but awfully unlikely that both motors would go bad in the same way at the same time, or that a mechanical problem would show up on both sides at the same time (although the drivers side door has only failed once, the passenger's side a dozen times or so) the fact that it once happened to the driver's side plus the fact that was right after a wash leads me to suspect the control module. so that's where I'll start this weekend and just see how the module looks.

I know this is a lot of info but I'm always open to thoughts or suggestions from anyone who has any ideas! I hope I can get this thing solved.

 

whew, I hope someone has enough patience to read all that! haha

 

I did. So what happened. Could it be caused by chicks sitting on your covers? j/k, I have the same problem and no one sits on my hood.

 

haha she was careful not to sit on the headlight itself!

I haven't been into this yet. I have been meaning to but other things always seem to come up and get in the way. the thing is this problem is pretty infrequent, its very annoying when it happens but its also so quick and easy to fix and it will be good for a few more days. all those things combined have put it lower on the priority list. one weekend coming up my plan is still the same. I want to disassemble the headlight mechanism and lube everything up, inspect for any damage or other signs, rotate the rubberish stops that the arms contact, remove and inspect the control module, look for signs of water intrusion, probably seal it up better one way or another...I just hope one of those steps cures the problem. if not I may have to start replacing pieces until the problem goes away.

 

Yes, I'm hoping it's rotating the plastic stop. Quickest and easiest.

 

Check to see if the motors are loose. There are several metal tabs at the base of the motors where they connect to the gear case. If they allow the motor to pull back slightly away from the gear case it will act like the gears are stripped. You can use a punch and tap those tabs in to tighten up the assembly. DON'T HAMMER IT, just tap until tight. It's easier with the motor and gear box on the bench. But you can tell if they are loose by just grabbing the motor and pushing it side to side. Rod

 

thanks! I'll add this to the list of things I'll look into. I really need to get this apart and figure it out so I can post up some results.

 

Keep me personally updated on what you find.
I posted the same problem and my thread all but disappeared.
I'm getting tired of having to turn the ****.

 

Have you looked at the gear in the motor. I just replace my left gear. My lights did some wierd things but now all is well. No teeth were broken, just a little wear on the gear from the worm gear.

 

I haven't checked yet but I replaced the stock gears with brass a couple of years ago. anything can happen but if I have a brass gear going bad, its the first I've heard of it. I haven't decided how far into the headlight I plan to dig yet.

 

I have almost the same setup as you... except I only got around to putting one gear in - on the passenger side. And it's a hardened aluminum instead of brass. I also have the 55w HID's.
Mine acts just like yours. If I back it off just a bit they open fine.
So, if you find a fix, I'll certainly be interested.
If I happen to get mine working, I'll post it up.