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Discussion Starter #1
For some reason my headlights don't work. When I check the voltage I have 12V on both leads at the bulb and my relay has 12V on 2 pins. I know that GM will use 2 positives to turn off lights sometimes. Has anyone seen this before
 

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First thing I'm thinking of, is if the lamp bulbs were easily accessible, you are working with the high beams lamps. Low beams are a tough nut to work with. I'll do some looking in the service manual, an either edit this post or add another post to assist in T/S your problem.

If your positive that the low beam headlight fuses F10 an F12 10A are OK, swap the low beam relay R6 with the high beam relay R11. these componets are located within the underhood fuse box. Then rotate the light switch to the headlights "on" position, an report the results.
 

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Are the high, low beam, or both headlamps not working? Presume as above you're referencing to the low beam headlamps.
 

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Discussion Starter #4
This is not an issue with no power its an issue with more power than needed. R6 and R11 are not the same size and are not interchangeable. Is there a reason I might have the lights off by 2 positives. Is there a reason the ground wood ever be positive?
Are the high, low beam, or both headlamps not working? Presume as above you're referencing to the low beam headlamps.
Yes everything else works as should. Low beams the only thing
 

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I recall the ground being switched, not the 12v supply.
 

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Do the low beam headlights work correctly when in DRL conditions ? I'll have to assume your low beam headlights were working correctly all along, until you posted this thread.. How long ago did they stop working ? Where are you reading this voltage that you feel shouldn't be there ? It looks like that if you had power coming from the DRL circuit (to illuminate the headlights in their somewhat dimmer mode) at the same time you manually, or the BCM decided to turn on the low beam in auto mode, you would have 12 volts from 2 directions (as best as I can understand the W/D) Which I think would zero out the net voltage on that low beam headlight circuit.. Sorry about the R6 an R11 relay idea.. I (obviously incorrectly) thought they were both the same P/N relays.
 

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Discussion Starter #7
Do the low beam headlights work correctly when in DRL conditions ? I'll have to assume your low beam headlights were working correctly all along, until you posted this thread.. How long ago did they stop working ? Where are you reading this voltage that you feel shouldn't be there ? It looks like that if you had power coming from the DRL circuit (to illuminate the headlights in their somewhat dimmer mode) at the same time you manually, or the BCM decided to turn on the low beam in auto mode, you would have 12 volts from 2 directions (as best as I can understand the W/D) Which I think would zero out the net voltage on that low beam headlight circuit.. Sorry about the R6 an R11 relay idea.. I (obviously incorrectly) thought they were both the same P/N relays.
I recently got the car and can't remember if they worked or not. I thought they did but I don't know. The low beams do not come on at all in any mode. I'm measuring voltage at the bulb connector and the relay connector 12V on both sides rather than 12V and ground. Ground circuit must be controlled by BCM and it is turning off the lights for some reason. What did you mean by dimmer mode?
 

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Drl as in daytime running lamps where the low beam headlights illuminate at less intensitsy i.e. in their dimmer mode.
 

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Discussion Starter #9
Drl as in daytime running lamps where the low beam headlights illuminate at less intensitsy i.e. in their dimmer mode.
No low beams. Even on drl. I ohmed 1 bulb but not the other its kind of hard to get to if one was out it wouldn't stop would it?
 

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Kinda hard to understand how you are not sure that the low beam headlights have ever worked, since owning the car. Lets eliminate a few things

1 >>>>> During daylight, with the headlights switch positioned in the auto mode position, start the car an verify that a green symbol located top center of the instrument cluster is illuminated (which indicates that the low beam headlights were commanded on an are illuminated at about the 70% level). If you get the green symbol but no headlights, there's one problem.

2 >>>>> With engine off, select headlights on with the rotary switch, an verify if the low beam headlights illuminated at full power. If not, another problem. Push that turn signal lever forward an see if the high beam headlights illuminate along with a blue symbol in the top center of the instrument cluster (blue symbol to advise you that you that high beam lights have been turned on). If OK pull the lever back aft to return to low beam function, then rotate the lights switch back to the auto position.
Based on the results we can move forward.
 

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Discussion Starter #11
Kinda hard to understand how you are not sure that the low beam headlights have ever worked, since owning the car. Lets eliminate a few things

1 >>>>> During daylight, with the headlights switch positioned in the auto mode position, start the car an verify that a green symbol located top center of the instrument cluster is illuminated (which indicates that the low beam headlights were commanded on an are illuminated at about the 70% level). If you get the green symbol but no headlights, there's one problem.

2 >>>>> With engine off, select headlights on with the rotary switch, an verify if the low beam headlights illuminated at full power. If not, another problem. Push that turn signal lever forward an see if the high beam headlights illuminate along with a blue symbol in the top center of the instrument cluster (blue symbol to advise you that you that high beam lights have been turned on). If OK pull the lever back aft to return to low beam function, then rotate the lights switch back to the auto position.
Based on the results we can move forward.
Kinda hard to understand how you are not sure that the low beam headlights have ever worked, since owning the car. Lets eliminate a few things

1 >>>>> During daylight, with the headlights switch positioned in the auto mode position, start the car an verify that a green symbol located top center of the instrument cluster is illuminated (which indicates that the low beam headlights were commanded on an are illuminated at about the 70% level). If you get the green symbol but no headlights, there's one problem.

2 >>>>> With engine off, select headlights on with the rotary switch, an verify if the low beam headlights illuminated at full power. If not, another problem. Push that turn signal lever forward an see if the high beam headlights illuminate along with a blue symbol in the top center of the instrument cluster (blue symbol to advise you that you that high beam lights have been turned on). If OK pull the lever back aft to return to low beam function, then rotate the lights switch back to the auto position.
Based on the results we can move forward.
1) i have green light on dash, no low beams

2) turning on lights, everything but low beams work, switching to high works fine blue light and lights come on.

3) replaced both low bulbs still no lights
 

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The bulbs you replaced were the H11 version correct ? If you say H9, then were back to you working with the high beam lamps (which you say were/are good). The low beam relay base "always" has hot battery bus power applied to 2 pins (30 an 86) When pin 85 becomes a ground within the BCM, it allows the 12 volts sitting at pin 86 to now energizes the relay when low beam headlights are commanded on. That allows pin 30 to connect to pin 87 an send the power out to power up the headlights.
Any way you look at it (unless some tricky wiring rework has taken place prior to your ownership) I feel that both low beam lamps are burned out (an you've been messing with the high beam lamps all along.
 

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Discussion Starter #13
The bulbs you replaced were the H11 version correct ? If you say H9, then were back to you working with the high beam lamps (which you say were/are good). The low beam relay base "always" has hot battery bus power applied to 2 pins (30 an 86) When pin 85 becomes a ground within the BCM, it allows the 12 volts sitting at pin 86 to now energizes the relay when low beam headlights are commanded on. That allows pin 30 to connect to pin 87 an send the power out to power up the headlights.
Any way you look at it (unless some tricky wiring rework has taken place prior to your ownership) I feel that both low beam lamps are burned out (an you've been messing with the high beam lamps all along.
I definitely know low from high. I installed Sylvania silver H11. The 2 12v on the relay had me worried I'm glad you explained that. 10A fuses are fine. Would the dome light being unplugged have anything to do with it? The reason I didn't know if they worked is that I bought it and it went right into the garage for brakes and front end work.
 

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Check the interior fuse panel and verify both fuse F21 and relay R11 are in place for the daytime running lamps. For what it's worth, a blown fuse will have power on one side but not the other. When testing fuses with a circuit tester or the like, be sure to test both sides. Disregard if prior knowledge. Begs the question whether the bcm is grounding pin 85 or not. Can remove a headlamp and check for a ground to verify one way or the other.
 

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OK !!! Time to jump to the ground return wires going from both low beam lamps. If the 2 low beam headlight ground wires going to their grounding location are faulty, there goes your lights. If the grounds are open at this time, when you meter read the 2 wires connected to the lamp (when headlights are selected on) to a ground source, they both would show 12 volts. Those 2 ground wires are routed too, and join up with a batch of other ground wires an bolted to the inside of the passenger side frame rail (approximately below the electronic brake control module).

You can verify the condition of either or both lamp black ground wires by looking for continuity to a known good ground source. If indication shows infinity (which is bad), maybe you can back stab the black wire at the 2 pin connector with a test wire attached to a good ground location. That should allow the lamp to illuminate when selected to on. If that works, you would have to hope that the ground wires are intact all the way to that normal grounding location. You would then have to gain access to that grounding stud ( on that frame rail) in hopes of finding some level of corrosion interference.
 

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Discussion Starter #16
When I pulled the fuses I didn't have voltage on either side. At first before I replaced the bulbs at the bulb plug-in I had 12v on both leads. Now I don't have any on either. I have not checked anything on the inside of the car yet. Thats next I guess. I hate working with a computer when you don't have a diagnosis tool. I will check all that. Thank you
 

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For info >>>>> all 4 fuses powering up the low an high beam headlights do not have any power to them, until their respective relays are energized.
 

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Probably a moot thought, but were the headlamps powered on while testing the leads?
 

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Discussion Starter #19
Ok so fuse ok inside. Relay ok inside. Measuring voltage at bulb plug-in when I first start it has voltage on 12v on one lead and ground on the other but light doesn't come on ??? After a couple of minutes in turns to 12v on both leads ??? The lights never come on at all ??? I'm down to thinking BCM but can't test without Tech2. Just wondering if anyone else has had this problem?
 

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Believing the circuit is functioning as it should, remove the R6 relay, an jump pins 30 to 87 on the relay base. This puts the 12 volts straight to the low beam lamps an they should/would/must illuminate. If they do not, there is a breakdown in the circuit.
Refering back to the headlights. There's a simple test to verify the ground wire connection for the headlights. With the 2 pin connector removed from the lamp, put the meter across the 2 pins, (with the meter set up to read voltage). Turn on the headlights, an you must read 12 volts. If not, remove the meters ground test lead from the 2 pin connector an connect it to the underhood jump grounding post. If it now reads 12 volts, that says that your ground wire is open somewhere in its run down to its grounding stud on the frame rail.
 
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