08 TB LT no low beams.. not the relay

[HTUSA]

Ok so I have a low beam headlight problem.
I have replaced the relay. No change. Yes with an AC Delco brand.
I replaced the fuse block. No change.
I get no power to the relay when they do not want to come on. I have checked with a multimeter.

Randomly my low beams will shut off. I am not sure what's next.
Thought it might be the the auto dim or daylight switch on the dash next to the window. I blacked it out with some electrical tape.
Anyone else has any other suggestions? I am at wits end.

Stock headlamps. Checked all connections at the lights nothing burned or out ordinary.

I have posted this before thinking I had it fixed. My fix worked for a while but now it's back. I just replaced the relay I replaced over a year ago. Thats when I replaced the fuse box. As I thought it might be the issue.

 

[Mooseman]

Have you downloaded the manuals in my signature and check the schematics? I'd be tracing wiring back from the relay and BCM.

 

[Up And Down]

Sounds like it could be the "darkness" switch next to the windshield like you said. Blacking it out with tape may not fix it if the switch itself is faulty. Does this happen only when in auto headlight mode? If so, that would steer me towards that switch. Have you tried using the low beams in manual mode and, if so, do they stay on? If you have not tried this yet I would suggest it as it will determine if it is only a problem with the auto headlight system or not.

 

[budwich]

Ok so I have a low beam headlight problem.
I have replaced the relay. No change. Yes with an AC Delco brand.
I replaced the fuse block. No change.
I get no power to the relay when they do not want to come on. I have checked with a multimeter.

Randomly my low beams will shut off. I am not sure what's next.
Thought it might be the the auto dim or daylight switch on the dash next to the window. I blacked it out with some electrical tape.
Anyone else has any other suggestions? I am at wits end.

Stock headlamps. Checked all connections at the lights nothing burned or out ordinary.

I have posted this before thinking I had it fixed. My fix worked for a while but now it's back. I just replaced the relay I replaced over a year ago. Thats when I replaced the fuse box. As I thought it might be the issue.

The "big point" here is your statement about "no power to the relay when they do not want to come on"... what are you trying to say?
The relay power wired to it via "b+" which is basically on at all times that your battery is connected to the system.
IF you are talking about the "control wire" for the relay... it is a PWM "energized" wire which you may or may not be able to see anything on depending on your meter and settings used to monitor it.

As you have perhaps surmized, the BCM is controlling how much "energy" is sent to the "relay" (FET actually) to allow for things / features like daytime running which requires reduced "on" time (less cycles) for the relay (ie. less "energy"). Of course, there are a few other inputs to the bcm to control its control of the headlights. IF as others have suggested, you can manually select the lights with the switch, then it is likely that the circuit from the bcm to the headlight relay is fully functional which leaves the "automatic/sensor" stuff going into the BCM.... BUT if it doesn't work, it could also mean a poor ground may be happening resulted in "flakey" BCM operation.
Other BCM operations working OK?

 

[Mooseman]

Do the daytime running lights work? What happens when you use the switch?

 

[HTUSA]

Ok to answer some more questions. The daytime running lights do work. They come on for a few minutes then go off.
Yes I have power to the relay but the "control wire" I do not.

Last night:
Drove during daylight into town for dinner. Come home.
TB sat for 2 hours before I went back out to monkey with the lights.
Went to manually turn the lights on.. nothing but parking lamps.
I had two good solid state relays, I changed them out and still nothing.

Every time this happens, I can not get them to manually turn on.

I am downloading the schematics now and hoping for a ground wire problem. I will pull the top to the BCM and make sure nothing is fried or out of order.

Everything else works fine in the TB. No other issues other than drivers side speaker cutting in and out, but I highly doubt that has anything to do with the lights.

 

[Mooseman]

You wouldn't see DC voltage at the relay control wire since it's a PWM unless it does give 12V+ when commanding full lights. So the BCM is supplying a PWM signal for the DRL but not for full headlights. I'd ohm out the wire from the relay control wire to the BCM (pink/white). As one last test before condemning the BCM, wrap a wire around the relay's control terminal, put it back in the socket and apply 12V+ to it. This should light up the lights full. (We do this as a mod with a diode to have all 4 on with high beams). If that works, then I would suspect the BCM.

Only one thing makes the lights work, the BCM, which receives a signal from either the light sensor or the switch to turn on. Maybe the switch or the sensor is defective, confusing the BCM?

 

[coolasice]

Randomly my low beams will shut off.

The daytime running lights do work. They come on for a few minutes then go off.

so DRL's are intermittent also?

 

[HTUSA]

so DRL's are intermittent also?

Yes on and off.
Tonight I took it out at dusk. Lights wouldn't flip on.
I covered the ambient light sensor and 5 minutes later boom full low beams. I left it covered and for the entire drive home they didn't flip off. It is sitting now. I will go try again in a few minutes.

 

[HTUSA]

Let me start by saying I went back out a few hours later and the lo beams would not flip on.
Ok so I have a video of my testing. I will post once at work. My upload speed sucks at home.
Anyways testing. I followed May03LT's troubleshooting and came up with this:
Pin 2 B+: Connected to the ground side of the battery, my test light comes on
Pin 6 Ground: Connected to the positive side of the battery, my test lights comes on
Pin 5 Control: Connected to the positive side of the battery, with the interior switch in the on position, my test light comes on. Switch off, test light goes off
Pin 4 Lights: Jumping it straight to the positive post, my lo-beams come on.

I am at a loss right now with what to do. The only thing that comes to mind is the solid state relay. I have two relays. One that is part store brand. The other is AC/Delco and I purchased it from the dealer. Part numbers match.
I have swapped them both with no change in the lights....
I could hot wire the relay with jumpers for giggles.
I wonder if both relays were burned out by the BCM or something. Maybe too much power. I dont know. Im grasping at straws now.

My wife refuses to drive this thing at night. Sigh...

Any suggestions?

Edit: Forgot to say.... Thank you all for the help so far. I really appreciate it.

 

[budwich]

IF your test light in "pin 5 test" (not sure which that is but you indicate "control" of the relay) is on "solid" / bright then that is your problem. There should not be a "solid ground" to allow the light to "fully light". The PWM duty cycle has some level to it... not ground... I think which a "full light" may be indicating.

 

[HTUSA]

IF your test light in "pin 5 test" (not sure which that is but you indicate "control" of the relay) is on "solid" / bright then that is your problem. There should not be a "solid ground" to allow the light to "fully light". The PWM duty cycle has some level to it... not ground... I think which a "full light" may be indicating.

May03LT's video shows the test light on with the switch in the on position and off with the switch in the off position. Maybe I'm not understanding you?

 

[budwich]

sorry... initially, I didn't have time to watch the video. I think that the video is good but not sure it provides the "full test". As I indicated, the "gate control" for the electronic relay is providing power to operate the "electronic gate". In the test displayed, the check is providing power via the battery to the test point / control pin. If the pin has a "circuit connection" of "some kind", power will flow from the battery thru that "some kind" and light the bulb... BUT that doesn't actually mean that the "some kind" has the power in itself to power the gate / control of the FET. So that test is somewhat OK to indicate that there is something happening in the BCM in response to the stimulas of light switch but what it doesn't provide is "knowledge" that it is totally good. However, it is somewhat likely that BCM is bad based on the results of your testing especially since you have tried two relays. Of course, that doesn't mean that the second relay that you got is actually good... some good "person" might have returned it and the supplier put it back in stock with out testing.

Ultimately, checks of the BCM functions via "test computer" is one way. Further, though a test of either the original relay or replacement relay put into a working system provides some assurance that the issue maybe outside that of the relay.... all assuming that you have thoroughly inspected the fuse box contacts to ensure that the relay contacts are indeed good. To that end, if you have time, you can try make up leads to "totally host the relay outside of the fuse box" (all contact in the fuse box have test leads running to the relay pins).... but be very careful on how your test wiring is run and held.

Hope that helps.

 

[Mooseman]

If both relays act the same, then likely the issue is outside of the relay.

Have you tried turning on the lights and wiggling the relay? It is possible that there is a bad/poor contact in the fuse box itself, possibly caused by heat.

 

[HTUSA]

If both relays act the same, then likely the issue is outside of the relay.

Have you tried turning on the lights and wiggling the relay? It is possible that there is a bad/poor contact in the fuse box itself, possibly caused by heat.

Ok I thought that as well. The relay was really loose and I could wiggle it and the lights would come on. Once I let go they would turn off.
I replaced the entire fuse box. Used of course, from a 2008 wrecked. (Rear end hit)

I wonder if its the connector underneath but I dont think it would get power to the B+ or ground if it were the plug.

 

[budwich]

take the relay pins and "gently" twist the pins so that they have a slight "angular twist" across their contact surface. That way when they seat with the fuse box socket, they will likely make contact with either the back or front of the socket copper plates.

 

[HTUSA]

take the relay pins and "gently" twist the pins so that they have a slight "angular twist" across their contact surface. That way when they seat with the fuse box socket, they will likely make contact with either the back or front of the socket copper plates.

That did not work.

I am looking for a TB to test my relays with... I would be really surprised that two of these are bad.

 

[Mooseman]

Or just go to a pick-n-pull and grab a handful. Earlier years were less prone to these failures. Grab the ones for the fan clutch (which '08 doesn't have). Same relay but less amps going through them.

 

[HTUSA]

Or just go to a pick-n-pull and grab a handful. Earlier years were less prone to these failures. Grab the ones for the fan clutch (which '08 doesn't have). Same relay but less amps going through them.

Good idea. The part store one comes with a lifetime warranty. I'll get it replaced and grab a hand full. I know of several TB in a couple junkyards now. Hopefully they have the relays still.

 

[HTUSA]

Fixed!!

Replaced the part store brand with a new one and fixed...
I stopped at the junk yard and picked it clean. Gathered 15 or so. Half being from 2003 or 2004 models. Total 5$.
Hopefully this will fix the problem. I think it will for a short time. I have used BWD electrical parts in the TB and end up replacing them within a few months. I have become proficient in changing out the ignition switch and HVAC blower resistor. LOL

Thank you all for the help.
I am tempted to take the AC Delco back to the dealership and tell them I want my money back. Pretty ticked about that one.

 

[Mooseman]

Part store brand relays have been known to either fail, melt or catch fire. ACDelco are the ones we usually recommend but obviously you got a dud. I already have a supply of the recycled yard ones.

 

[coolasice]

There's a warranty extension for the 08-09 trailvoys.. I got the letter in the mail,. Think it said 12yrs or 150k miles. For the lowbeam headlights,. Something like that. GM will reimburse if you fixed yourself also.

 

[Mooseman]

Yep, it's a fairly recent announcement although they've had issues since 2014:
http://www.detroitnews.com/story/bu...05/11/general-motors-investigation/101554484/
https://www.carcomplaints.com/news/2017/gm-headlight-warranty-extended.shtml

Wonder why they started going bad in 2006? Maybe a bad batch/cheaper modules/relays? Cheaper wiring causing higher amps? I had the original in my 02 EXT and it never failed in over 300k km.

 

[Mounce]

Yeah I definitely wouldn't recommend using the parts store relay. This is what they can cause, not always but possible.

 

[HTUSA]

Called the dealer. I got my money back for my fault one, then he handed me a new one. I took my part store one back and got my money back on it.

With the extras I have and what now I hopefully and good to go now.

Thanks to all for the help. I am not an electrician