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Author Topic: high beams work, low beams do not  (Read 11955 times)
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Jusmarty
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« on: 06/04/05 07:16 AM »

Yesterday, when I drove my 2002 z-71 at night the automatic headlamps turned on, but the low beams failed to light up. parking lights-OK, fog lights-OK, high beams-OK, negative low beams. Went to the local chevy dealer for some tech advice after I pulled all fuses that were part of the headlight system and found them to be OK. I replaced both headlights, still negative lights. Replaced the control box on the dash that controlls auto hdlght, and manual override, still no low beams..... ANy advice on the next step???\

I am a good parts replacer.....

Justin
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« Reply #1 on: 06/04/05 07:25 AM »

relay
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« Reply #2 on: 06/04/05 08:09 AM »

The relay switches both in an 02 and fuses are common for High & low, per side.. The dimmer switch is your likely culprit.

Here's a diagram. It expands; how, depends on your browser.
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« Reply #3 on: 06/04/05 08:45 AM »

Thanks for the info!!!!!!!!!
Next ??
How difficult is it to change out the dimmer switch??\
\
Justin
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« Reply #4 on: 06/04/05 09:15 AM »

I would have to dig for it, but as far as the column parts go, here's one for the 02 ign Sw R&R.
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« Reply #5 on: 04/28/06 05:59 AM »

New to this thread, thanks in advance for your help, I own an '02 1500 4wd, can't figure out what's wrong with my low beams...went from occasionally flickering to not working at all...

fuses ok, replaced multi-functions switch, swapped out relay, no change

someone mentioned dimmer switch, is this the dash light dimmer??

voltmeter shows no power at lo beam terminal, it shows power when i run the negative prong to ground....

hate to resort to the dealer..

highs work
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KY_BOB
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« Reply #6 on: 04/28/06 06:22 AM »



someone mentioned dimmer switch, is this the dash light dimmer??



no

Most likely it is the dimmer switch.  The dimmer switch is mounted to the steering column under the dash and connected to the lever that you pull to dim your lights be a rod.

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« Reply #7 on: 04/28/06 07:15 AM »

thanks KY Bob for your reply, I think I'm calling the dimmer switch the multi function switch,(hi lo, turn signals, cruise, wipers etc), this was all electric with plugs into bus, no rod to activate a switch although I know what you mean as I've seen those in older gm vehicles...

it seems like I'm not getting a ground for the lo beam circuit, is this ground independent of the high, because the highs work... if they share a common ground it blows my theory....
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« Reply #8 on: 04/28/06 09:02 AM »

thanks KY Bob for your reply, I think I'm calling the dimmer switch the multi function switch,(hi lo, turn signals, cruise, wipers etc), this was all electric with plugs into bus, no rod to activate a switch although I know what you mean as I've seen those in older gm vehicles...

it seems like I'm not getting a ground for the lo beam circuit, is this ground independent of the high, because the highs work... if they share a common ground it blows my theory....

I didn't realize that they had changed the dimmer switch set-up?


This applies only to 2002's not the later models.

I can tell you for sure that there is a separate ground wire for the low beam lights.  Breaking the ground is how the trucks kill the low beams when the highs come on.  I have probably done the all 4 on high mod on at least 10 2002 AV's and the way that mod is done is to give the low beam a permanent ground wire instead of just the one controlled by the truck.

If you'll search the A4OH mod there are plenty of pics of this mod.


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« Reply #9 on: 04/28/06 09:14 AM »

The "Dimmer" switch section of the multifunction switch, to be more specific, is the common culprit in the 02. It simply switches the ground "return" of the headlamp filaments. One or the other.

As KY_BOB mentioned... "A4OH"

Before you tear into the column and replace it, just do the 02 version of the All4OnHi mod. That's a "permanent" ground connection of the lowbeams, where they will stay on when you switch on the highs.

The headlamp power source is switched on by the relay, which is independent of the high & low beam switching. In this case, you would still retain the normal headlamp on/off function.

Good luck!
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« Reply #10 on: 04/28/06 05:45 PM »

sounds as if the A4OH modification is the way to go, I'm going to attempt that this weekend

I already swapped out the dimmer switch and nothing changed, luckily, the dealership agreed to take the return (brother in law with an inside contact) so at least I'm not out the $230 for the switch

thanks again for your input/response, this site is a great resource, I'll keep you posted on how it turns out...

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sperry
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« Reply #11 on: 04/28/06 07:13 PM »

It could be the connector pin under the UBEC (Underhood Bussed Electrical Center). A GM Technician member mentioned he experienced many of them in the 02 & prior GM trucks.

Look for a burned or corroded terminal(s). Particularly in Connector 1 and Connector 4.

My 02 electrical centers doc doesn't show the connector colors.. Sorry! (Just check them all.)
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« Reply #12 on: 04/29/06 09:42 AM »

Thanks for the heads-up Sperry. Is this underhood electrical bus (UBEC) the one mounted just inside the drivers side fender?
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« Reply #13 on: 04/29/06 05:25 PM »

Never could find the culprit for the low beams not working, I did the a4oh mod as described and now all is well. I checked the prongs where the green 'bus' plugs in and didn't see anything unusual. Didn't pull the top halve cover of the ubec, so I guess there could be a problem there. There is continuity between the yellow plug and the light socket, so I guess the problem is between the bus and the switch somewhere.

Either way, I've got my low beams back. Again, a big thanks for all the good advice. Now, on to finding out how to solve a knock sensor triggered service light....
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« Reply #14 on: 05/01/06 06:24 AM »

Never could find the culprit for the low beams not working, I did the a4oh mod as described and now all is well. I checked the prongs where the green 'bus' plugs in and didn't see anything unusual. Didn't pull the top halve cover of the ubec, so I guess there could be a problem there. There is continuity between the yellow plug and the light socket, so I guess the problem is between the bus and the switch somewhere.

Either way, I've got my low beams back. Again, a big thanks for all the good advice. Now, on to finding out how to solve a knock sensor triggered service light....

Glad that worked out for you. Cheesy   + The extra light when on high beam is nice.

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« Reply #15 on: 05/01/06 01:52 PM »

Thanks for the heads-up Sperry. Is this underhood electrical bus (UBEC) the one mounted just inside the drivers side fender?

Yup, the big electrical box under the hood.

Regardless, at least you have the nice All4OnHi lighting now! Smiley
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« Reply #16 on: 05/01/06 02:59 PM »

Yeah, the extra light is nice. I wish I had known about this mod before. I do a lot of towing on two lane country roads after dark, gonna be a lot nicer now!! Thanks again!
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« Reply #17 on: 05/26/09 07:27 AM »

I did this mod a few years back and it fixed the problem.  Now the same problem is back.  Any updates for where to look for the culprit? 
"the connector pin under the UBEC (Underhood Bussed Electrical Center)"   What does this look like?  Anyone with a digital cam care to show me?  I'd hate to have to pay someone to do the work for me!

Thanks!
Shawn
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« Reply #18 on: 05/31/09 11:08 AM »

My low beams just stopped working too, but they do work when the steering wheel is tilted all the way up.  When i tilt the steering wheel down, the low beams go out.  Any suggestions? 
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« Reply #19 on: 12/09/10 04:57 PM »

I know this is an old thread but I didn't see any need to start a new one.

I did this mod a few years back and it fixed the problem.  Now the same problem is back.  Any updates for where to look for the culprit? 
"the connector pin under the UBEC (Underhood Bussed Electrical Center)"   What does this look like?  Anyone with a digital cam care to show me?  I'd hate to have to pay someone to do the work for me!

Thanks!
Shawn


Same thing happened to me tonight.  Maybe I've had one low out and hadn't noticed it until the other went out?  Any better ideas?  It's too cold to mess with it tonight.  I've had the A4OH mod for years, I'm sure it isn't losing ground.   I'll look into it this weekend.  Any input is welcome.


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« Reply #20 on: 12/09/10 05:40 PM »

I know this is an old thread but I didn't see any need to start a new one.


Same thing happened to me tonight.  Maybe I've had one low out and hadn't noticed it until the other went out?  Any better ideas?  It's too cold to mess with it tonight.  I've had the A4OH mod for years, I'm sure it isn't losing ground.   I'll look into it this weekend.  Any input is welcome.




Well, I have my answer to my question.  (Yes, I said it was too cold but I couldn't stand not knowing).

I had one blown bulb, not a biggie.  The other side has a burned plug.  I moved the good bulb to the good plug and I have one low beam.  Guess I have to find a replacement plug.  Anyone ever heard of that one? Huh
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« Reply #21 on: 12/09/10 06:47 PM »

Hey Bob

I would doubt it was caused by the A4OH mod, probably just corrosion in the plug. When you get the replacement Plug(PigTail is what the may call it) put some dielectric grease in the plug to seal it so no water or mist gets to it.
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« Reply #22 on: 12/10/10 08:44 AM »

Hey Bob

I would doubt it was caused by the A4OH mod, probably just corrosion in the plug. When you get the replacement Plug(PigTail is what the may call it) put some dielectric grease in the plug to seal it so no water or mist gets to it.

Ordered the bulb and socket from the local parts store. (they never have anything in stock but they can always "have it for you in the morning")  They will have them both in the morning.  I plan on cutting, soldering, and heat shrinking the new pig tail on to the harness. 

The dielectric grease is a good idea.  Thumbs up!  I have some but never thought about using it on something like a headlight plug.  I'll do that.
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« Reply #23 on: 04/02/13 08:02 AM »

Greetings!

Newbie here and thought I might revive this thread, in that it is exactly my problem today. Started out with low beams shorting out when I operated the steering column up and down. When it finally hit a "sweet" spot, they remained on until I switched off the engine.

Seems to me that pulling and letting slack into the wiring harness has always been the culprit. Determining exactly which wire or plug is the order of business here. Something is losing contact INSIDE the cab of the truck! I have yet to figure out where between the steering column and the dimmer switch I am supposing.

Any more ideas here or guidance?

Thanks!  banghead
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« Reply #24 on: 04/02/13 05:29 PM »

Somewhat related.....on my 2002 if both your high beams burn out the high beam indicator will be lit when you have the high beams off and when you switch the high beams on the high beam indicator goes off, with no headlights. Happened to me once. I thought that I had lost the low beams since the only time I had lights was when the high beam indicator was lit, but I really had low beams at that time.
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