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12-13-2011
Just to let you know the "temporary fix" I posted days ago ended up not working. I still have no idea what the issue is. I'm taking it to a dealer tom morning. Sawt711, did you have any problems or possible causes leading up to them not working? Just curious.
12-14-2011
Finally got it fixed! It was the head lamp module. I guess it was shorting out. Cars are endless cash pits...
12-05-2012
Sounds exactly like what is happening with my daughter-in-laws car. Does anyone know where the headlamp module is located???
12-05-2012
The headlamp module is called the HDM relay. It's in the underhood fuse box.
I applozgize for not seeing this thread sooner. That's always the problem. drls and low beams don't work it needs a new one.
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12-06-2012
So it was the relay I told you about!! LOLOriginally Posted by Dre Man
12-06-2012
Well in may case that relay has been changed twice and is NOT the cause. Headlights go out intermittently at night. I'm thinking it is the daylight sensor on the dash but have not had time to work thru it yet
01-02-2013
My 2006 Grand Prix is doing the same thing. Everything works but the low beams. We have checked the fuses, bulbs, hdm relay. We also used the test light to see if fuse 3 and 4 get light and they do. I don't know what else to do. Could a corroded battery cables and posts cause this problem. Any advice would be appreciated
01-03-2013
Does it always do it or intermittingly? if intermittingly, I would change the HDM relay.
01-03-2013
I am still having all the same conditions you have mentioned with my Daughter-in-laws 2006. I have replaced the ambient light sensor on the dash, the HDM relay twice, cleaned all the grounds. Have not replaced the headlamp switch or the Body Control Module. I found a wiring schemetic for the car and all things feed into the BCM and the BCM triggers the headlamps. So I am now driving the car as fate would have it they have worked perfectly the past week or so. My plan is to check for power at the C1 terminal on the BCM next time the lamps go out. That is the terminal which feeds the relays. If there is no power there then I'll replace the BCM to see if that fixes it. Used BCM's are around $100 so I'm not going to just replace it for kicks. I'll let you know what I find whenever it fails next. This is surely a problem that is not easliy resolved!
01-03-2013
SnipImage.JPG
Don't know if you can enlarge this, or maybe you can copy it, but here is the wiring diagram for a 2006 GP daytime running lights and automatic headlamps
01-04-2013
It does it all the time. Last night it would not even crank. I had to get it towed. It didnt start with a jump start. Everythng on the inside went out except the lights. Even the power locks. Does this sound like a battery issue? Ive been told my posts are corroded.
01-05-2013
I dont think corroded battery posts would make the low beams not work. But if your car dosent wanna even crank, then you have other issues as well. how old is battery? We already replaced the battery 3 times in our 04. It has 130,000 miles now. And i always clean the terminals really good with a drill with a wire brush on it. (wear safety glasses). do you have the top post terminals on your 06? Iv always had problems getting them tight. I had to hammer them on the last time.
03-13-2013
I to once had interment low beam on a 2006 Grand Prix. The HDM module did fix it. It’s been about a year or so now. Now they are stuck on. I can pull the HDM module and they go out. There are no parking lights or taillights while on auto. If I turn it to manual then all lights work as expected, high/low, and parking/tail. As I am typing this, I wish I would have look this morning as I drove to work to check if when the car was running and selector in auto, did parking/tail work. I hope, it was dark. :-)
Talking to a friend last night, he pulled up the wiring diagram and either he or I was looking at it wrong but what he was saying did not make sense to what I saw. Then I found the snippet in this thread and it looks like what he is saying. If I remember right the under hood fuse block number up the left and letters are to the right. According to this threads snippet there is a Low (35) and High beam (34) relay. On mine the 35 is labeled HDM Module. On the threads snippet it looks like there are 4 prongs, one in each corner. The middle (B column) is blank. On mine there are three across the top (row 12) there are 3 prongs (column A,B,C) and 1 prong on row 11 column B.
I am assuming there is a different diagram, Any thoughts? I do have the VIN if that helps.
If the major blocks are still the same, then it looks like the BCM supplies ground (output) to the relays in the under hood fuse block. The turn signal switch grounds the inputs to the BCM. I am going to guess that since everything else seems to work, it’s not the turn signal switch. If that assumption is correct then it has to be the either the BCM or HDM. I am praying that it is the HDM. I did not realize that they switched ground and not power. I was using my test light connected to ground. I did find power on the A12. I guess I need to clamp to power and look for ground. “Synergy LS” or anyone else, do you have the diagram for the model I described?
Also, for about a week prior to the lights sticking on, they were slow to come on.
(After I posted this, I looked at the HDM module and it had a diagram. So..... More thoughts/Questions
sm hdm diagram.jpgsm hdm pins.jpg
Pin 2 = A12
4 = B12
5 = C12
6 = B11
So pin 2 is power, looking at the pull up resistor?, then does 5 go to the BCM? Then 6 would go to the low beam fuse? What is 4?
Last edited by penright; 03-13-2013 at 08:44 AM. Reason: Added Information
03-13-2013
A12 is power
B12 is headlamp low beam
C12 is bcm lamp control
B11 is ground.
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03-13-2013
Sent from my SPH-L710 using Tapatalk 2
03-13-2013
First Thank you so much. I am waiting for a friend to look up where the BCM is, if you don't mind me asking and so there would be a record of it here, Where is the BCM? I want to pull the plug just to make sure I don't have a chafe wire shorting ground.
Another question, has anyone had any experiences with the "knock off" BCM's? Or should I stay with AC Delco? Local part's stores are about $250 for AC Delco and Amazon has them for $160. I found some knock offs for $80. I can get the new one programmed (if that is what is bad) pretty cheap (like may just the cost of a steak dinner) if I expose it before I bring the car in. But I don't want to impose on my friend too much. I probably will go with the AC Delco.
Also, In the more information than anyone may care category...
I found the electronic symbol, it is called a "single gate enhancement mode mosfet"
Here is a hello world circuit to light up a led. So this is what I would describe as a "solid state" relay. It look like the work is done between pins 2 and 4 in our case.
03-13-2013
Bcm is left side of the dash. If you pull off the left side cover you can visibly see it. Youll need to remove the bottom panel to unplug the 3plugs and remove it.
What exactly are you trying to figure out? Hdm's go bad frequently or at least I see it alot. They aren't exactly cheap.. You can go to a junkyard and pull one from a prix or trailblazer for probably a few bucks
And yes there is a descreptcy between the years and correct diagrams.. The one i posted is correct.
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Last edited by rperry435; 03-13-2013 at 08:21 PM.
03-14-2013
My lights were stuck on. I could pull the HDM and they would go out. I was trying make sure the BCM was not holding the line low or a wire was shorted to ground. It was within a few years that I have replaced the HDM for lights not working. With your post of the actual pins (A12 is power,B12 is headlamp low beam,C12 is bcm lamp control, B11 is ground) that is what I needed. Before that I was trying to reverse engineer the schematic on the HDM, to figure out the pins. Which by the way after getting the information from you, I was able to confirm my BCM was working and no wires were shorted. Then again with your information, I ohm between 2 and 4 and there was a dead short. Then went to the parts store, verified the new one was open between 2 and 4 and it was. So $35 and I was fixed. I am so thankful God did answer my prayer :-).
Found it, got confused at first, it is exactly where you said, at first I looked up under the dash, but it more toward the rear, away from the firewall. After dropping the bottom panel, crawling under the dash, there is a connector that has a green lever that lifts the connector off of the BCM. I did not go any father since it was not my problem.
There is something I am missing here. According to the post with the pins (A12 is power,B12 is headlamp low beam,C12 is bcm lamp control, B11 is ground), which is correct, does not seem to match the two diagrams that I see in this post. In the 2006 and 2007 C12 goes to the headlamp fuse and it is the control from the BCM. Am I looking at the wrong diagrams?
Again, thank you so…….. much. You saved me lots of $$$$$$$$ :-)
12-10-2014
I am having similar problems with my 2007 Grand Prix. I replaced the HDM module and immediately got a check engine light with code P0033. Any ideas?
12-10-2014
P0033 has nothing to do with the headlights. You out of random got a code for something else.
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