vipmiller803

Hello all,

Having an interesting problem and a bit of trouble diagnosing the cause. Please forgive the long thread, but I have done a good bit of diagnosing with this, to no avail thus far.

A few months ago, an extremely intermittent problem started with the headlights not coming up, and it has been getting more and more persistent.

Headlights always turn on, which, from reading previous posts, tells me it is not the switch. (I do not use the twilight option by the way, but the symptoms were at one point replicated using that option to confirm manual switch abilities).

Here is where it is at now:
--Headlights almost always pop up when car is cold, engine running or not. It is not 100%, but I would say probably 95% of the time.
--Headlights often pop up when car is warmed up and engine is off. Probably around 80% of the time.
--Headlights often do not pop up when car is warmed up and engine is running. Probably around 50% of the time.

I have had instances where I would go somewhere and stay for maybe an hour or two on a warm summer night. Come out and start the car, only to find myself headlightless. After a few failed attempts (turn headlights on and off), shut the car off, turn on headlights, start the car and on my way I go.

Again, the lights always come on, just fail to pop-up.


Now, onto the diagnosing:
--My first thought was, of course, the switch, but seeing as how the lights have no trouble turning on, I do not believe that is the issue. Please correct me if I am wrong.
--Second thought was the headlight control module. Took it out and realized it has opened up on the back end like many have. Took a gander around the board itself and no real dark black marks, so I reflowed the high power contacts on the relay and the mosfets and put it back together. No change.
--Decided to clean up the four main grounds in the engine bay. Full cleanup with all connections steel brushed. Put back together. No change.
--Took the module back apart, did a lot of voltmeter testing with the circuit board attached to the car. That was when I discovered the difference between the car running or not. Normal battery voltage at the module was measured. Voltage is getting to the signal on lead every time just as one would expect. Two different times, I had the headlights on and the on lead (on the module circuit board) had battery voltage, but the headlights stayed down. I decided to be absolutely sure that that was not a weak on signal coming from the headlight switch, I would connect it directly to the battery positive terminal. Measured amperage. It drew almost two amps, but headlights stayed down.
--Decided to replace mosfets with new ones, thinking that could be an issue. Did a whole cool somewhat documented heat sink on the new ones. No change.
--Took the module apart one last time to finally check the relay contacts. Didn't do that before thinking the headlights always closed just fine, which is when the relay actually functions and is most susceptible. Two of the leads were darker than the others, but all the contacts were clean. It is a four lead two throw relay, and if just one of the leads fails, it would leave the other headlight functioning just fine. Not the symptom I have.
--Decided to just replace the module with a sourced one just because diagnosing that unit further might bring me to insanity. No change.


Food for thought:
--The higher system voltage while engine is running and the general warmth of the engine bay seem to be the main variables affecting the symptoms. Tried to simulate the ~14 volt system voltage using a battery charger. Limited and unreliable results keeping the headlights down.
--I thought about maybe there is a high resistance area either in the power line or the signal on wire on the way to the module getting affected by heat enough to make the module fail. I think my tests covered that. Also, the module gets one positive line per headlight motor, so only one of those would be affected at a time.



I am a little stumped, and I am not the type to be at all. I have plenty of electrical experience and consider myself quiet the tinkerer.

Cliffnotes version:
Not the switch, headlights come on.
Not the module, replaced and symptoms prevail.
Not the module ground, cleaned and measured operating voltage at module leads.
Not signal wiring, signal gets full battery voltage and checked manually also.

What else could it be?

SilverC54me

Check the headlight motors directly. The are permant magnet motors that do have brushes that will wear out.
Also, there are no limit switches for the up down. So, if the motors have an excessive current draw the control module will stop the motor, i.e.. Remove power.

Gary

lionelhutz

There is a dark green wire on cavity C of the connector that is only powered when the headlight switch is off. Maybe it's staying powered?

vipmiller803

This is an interesting avenue. I suppose I can power the motors directly and measure current, but I believe the module treats the motors as separate and does not necessarily pull power simultaneously for both, so if one is drawing too much, then it would fail on its own.

Nevertheless, anyone know what the current should be for motors moving vs. motors working against their mechanical limits?

vipmiller803

That is the signal off line. I believe I checked that previously but will test it again while replicating the symptoms. If that is the case though, then that can be either the switch or the BCM right?

vipmiller803

I realize now I never updated this, so here it is if anyone runs into this in the future. I believe the problem turned out to be external to the board. I suspected this once the replacement board did not help the issue. I got a stalling after startup problem a couple of months after this popped up and decided to eliminate the ignition switch as a cause. Opened it up and cleaned the contacts. The battery terminals also had a little slimy buildup on them I did not like. Between those two corrections, the headlights never misbehaved again.

Beach18

Vipmiller803, Just read this thread. I have the exact issue on my 2000 C5. Exact.... Been an issue off and on for years, but since it was so intermittent, I didn't pursue it so much. I am very curious as to how yours ended up. Last night, I ended up driving home from a night car event with only the left side up. The right side would not come up, however; it was illuminated. I suppose I could have manually cranked it up, but chose not to. When I pulled into my driveway, I thought to throw my ball cap over the DRL sensor and may have actually made slight contact with it. The engine was still running and left right side was still down, when I recycled the switch. To my surprise, they both popped up as normal. Today, I took a look at both sensors (DRL on the right and the a/c sunlight sensor on the left) on the dash grille. No obvious signs to note and this vehicle is a very low mileage car never stored outdoors and with little time in the sun overall. Both motors work fine and both have had the gears replaced with success. As you, I don't believe it is my multi-function switch and my twilight option is off. Did you ever solve this mystery, or like me, are you still guessing my way to a correction?

Autoeng

Hello Beach18,

Did you see his last update? It appears he identified the factors causing the issue.

Beach18

Autoeng, Thanks for the reply. I did see that thread, but was hoping to know if he had any reoccurrence since then. This would add confidence to a solution for me. My pop up issue is so intermittent that it's hard to determine whether a fix actually worked except when it occurs. if his never malfunctioned since his fix, maybe that's my issue as well. I just hate chasing parts as a means of troubleshooting.

Autoeng

Well, what worked for him doesn't cost any money (cleaning contacts) so it wouldn't hurt to try and if not successful you can then start chasing parts. Last time he was on and posted was March. He may drop in occasionally though.

Beach18

Agree with your thought process. After removing and replacing (same parts) the DRL and Sunlight sensors, all headlights are working. Don't have confidence in this "fix", but will wait to do the ignition switch procedure. Battery is new, so no issues there and this headlight problem was occurring way before the battery was replaced. If the problem resurfaces, I will check the ignition switch as suggested. Was just thinking that those sensors, or one of them could be the issue. The pop up problem seems to only occur after dark. When I check during daylight, it doesn't happen, but that also could be a coincidence. It's a game of patience, I guess. I like to think I am more of a diagnostician more than a parts changer, but we'll see. Thanks again...