Headlight problems

2000 GMC Jimmy 4.3L 2WD SLE I just started having problems with my automatic head lights. Started the truck the other night and no head lights. All the other running lights were good, but no head lights. The high beam lights come on but not the low beam lights. I played with every button, dimmer switch, Dome Override, and even turned off the engine and restarted, nothing. I kept on pushing buttons and nothing worked. I sat there getting pissed and then they just came on. I know there is a photocell sensor on the passenger side of the dash in the speaker but it was dark outside at the time. The Multifunction switch in the steering column was replaced once before by a dealship under warranty so it is not the original factory installed MFS but should be OEM. I did check the ground that is located under the driver's head light and it seem good and tight. Anyone seen or had this issue? The lights do seem to eventually come on, but this is a pain in the @$$.

2000 GMC Jimmy 4.3L 2WD SLE I just started having problems with my automatic head lights. Started the truck the other night and no head lights. All the other running lights were good, but no head lights. The high beam lights come on but not the low beam lights. I played with every button, dimmer switch, Dome Override, and even turned off the engine and restarted, nothing. I kept on pushing buttons and nothing worked. I sat there getting pissed and then they just came on. I know there is a photocell sensor on the passenger side of the dash in the speaker but it was dark outside at the time. The Multifunction switch in the steering column was replaced once before by a dealship under warranty so it is not the original factory installed MFS but should be OEM. I did check the ground that is located under the driver's head light and it seem good and tight. Anyone seen or had this issue? The lights do seem to eventually come on, but this is a pain in the @$$.

Rick I do not have much good info from mitchell on them.
A All data online DIY SUB might help/have some good repair info on them.
I would get some one to read out and check body computer for problems.
Also connections and plug ins on it and headlight system.
And correct headlight bulbs.
Post back any body computer codes.
Also make sure sensor is open good not covered up.
Let us know how it goes.
MT

Thanks MT, I'll see what I can find. The bulbs are good because they eventually do light up, and I haven't changed any bulbs for over a year. I guess it is possible that something jiggled loose.

I suspect it is something to do with the Photocell. The problem is sporadic, as the low beam lights sometimes light right up when you turn the key, other times it takes a second for them to light up, and other times it takes a minute or two before they come on. One thing that I have found that does seem to work is to turn the high beams on then off a couple of times and it may be coincidence, but the low beams will come on once the high beams go off.

I can't believe that I am the poster child for things that no one has ever seen before.

I can't believe that I am the poster child for things that no one has ever seen before.

A quick fix my Dad had to do on his 2000 Buick which had the same problem;

He put a piece of tape over the sensor, to keep his lights always on.
The Dealership wanted $500.00 to replace the dash unit (parts & labor), so that piece of tape stayed on for over a year (he traded the car in last June)

He also had a faulty brake light/ABS sensor problem.
$700.00 repair bill (Again, dealer replacement- ABS unit).

Sorry, no advice.
Just wanted to let you know, you're not alone.
:iceslolan

He put a piece of tape over the sensor, to keep his lights always on.
The Dealership wanted $500.00 to replace the dash unit (parts & labor), so that piece of tape stayed on for over a year (he traded the car in last June) :iceslolan

I have thought about doing the tape trick if it would work. I am wondering if the photocell unplugs and could be jumpered or just left unplugged to achieve the same thing.

I have thought about doing the tape trick if it would work. I am wondering if the photocell unplugs and could be jumpered or just left unplugged to achieve the same thing.

I'm gonna take a wild internet warrior/no experience guess and say, if you remove the plate that the sensor is attached to, remove the connector and install a jumper in it, that should do the trick.
Unless of course, it's a 3 wire or more connector.

The photocell itself is just a switch that either opens or closes the circuit dependant on light, so it may be worth a try.

Try the tape first though.

I'm gonna take a wild internet warrior/no experience guess and say, if you remove the plate that the sensor is attached to, remove the connector and install a jumper in it, that should do the trick.
Unless of course, it's a 3 wire or more connector.

The photocell itself is just a switch that either opens or closes the circuit dependant on light, so it may be worth a try.

Try the tape first though.

I'm trying to find a diagram of the Photocell circuit to see exactly what it looks like (how many wires etc.) and exactly what it is called. Any Ideas?

I'm trying to find a diagram of the Photocell circuit to see exactly what it looks like (how many wires etc.) and exactly what it is called. Any Ideas?

Rick if you are going that deep in it.

A factory repair manual or all data diy online sub.

http://www.alldata.com/products/diy/index.html

Rick if you are going that deep in it.

A factory repair manual or all data diy online sub.

http://www.alldata.com/products/diy/index.html

Thanks MT, here is another update. I could not find any Photocell information online because it is listed as a Sensor. A quick call to my local Dealership and found out that the GM part number is 12450120. It costs $14 USD. The unit itself has two wires and the actual sensor snaps on and off with a standard plastic clip found on just about all GM connectors. All that being said, it was not the problem. I replaced the sensor and still had the same issue with the low beams not wanting to light. I was giving up for the evening, pretty pissed that I spent the $14 and slammed the Hood shut, and the *#@&)#!% lights came on! I opened the hood back up and proceded to check the grounding wires. I found 4 different grounds, one on the negative battery cable to the block, one from the battery pigtail to the frame, another one from the second battery pigtail located under the passenger's headlight, the fourth one under the driver's headlight. All were tight and I tightened them again to be sure. The peculiar thing is that the High Beams work all the time when I pull the turn signal handle.

I am not sure if there are anymore grounding locations, any suggestions?

One thing the guy at the parts counter said was the ECM tells the headlights when to turn on and off. Where is the ECM Ground wire?

Thanks MT, here is another update. I could not find any Photocell information online because it is listed as a Sensor. A quick call to my local Dealership and found out that the GM part number is 12450120. It costs $14 USD. The unit itself has two wires and the actual sensor snaps on and off with a standard plastic clip found on just about all GM connectors. All that being said, it was not the problem. I replaced the sensor and still had the same issue with the low beams not wanting to light. I was giving up for the evening, pretty pissed that I spent the $14 and slammed the Hood shut, and the *#@&)#!% lights came on! I opened the hood back up and proceded to check the grounding wires. I found 4 different grounds, one on the negative battery cable to the block, one from the battery pigtail to the frame, another one from the second battery pigtail located under the passenger's headlight, the fourth one under the driver's headlight. All were tight and I tightened them again to be sure. The peculiar thing is that the High Beams work all the time when I pull the turn signal handle.

I am not sure if there are anymore grounding locations, any suggestions?

One thing the guy at the parts counter said was the ECM tells the headlights when to turn on and off. Where is the ECM Ground wire?

Lot of grounds on ECM.
All Data online sub wiring diagram shows all grounds.
For the ground circuits you need a good wiring diagram.

Usually the body computer has first control on Day time running lights them.

Engine Oil pressure switch may work threw the ecm to body computer to tell the body computer and daytime running light module the engine is running or not running.
Also park brake light switch is tied in there to.

ON ECM grounds look for the black wires.

C1 pin 17/18
C2 pin 17/18

ECM grounds are connected to/grounded to black ground wire Right rear cylinder head

O.K. here is another piece of information. The lights coming on after slamming the hood got me to wondering about the Headlight Relay. The Relay/Fuse panel is located over the driver's wheel well inside of the engine compartment, just under the hood, which I think would be probably be jostled around when the hood is slammed. I opened the cover and it appears that the Headlight Relay is located at the front of the panel, closest to the radiator. The diagram inside the cover of the panel shows a relay marked HDLP PWR. I assume this means HEADLAMP POWER. I tapped on in and wiggled in its socket but I decided to see about a replacement before trying to remove it (and possibly break it). Here is the funny thing, since I did this on Friday afternoon, the headlights have worked properly and not given me anymore trouble. I talked to a parts guy at the local parts store and they did not have any replacement relays, but he did say that traditionally, relays are either good or they are bad and there is no sporadic function with these things. Well I don't know, considering that I am a poster child for things that no one has ever seen before in the entire history of automobiles, I am hoping that my problem was a dirty socket or some other minor issue, but for now, I am going to keep a close watch on this and see what happens.

Well, I knew it was too good to be true. Last night and again this morning I had no headlights when starting the Jimmy. In both cases I carefully opened the hood with the motor running and lightly tapped on the headlight relay and instantly, the head lights came on.

What I don't know is whether I have a bad relay or possibly a dirty socket. I guess I will stop at the dealership on the way home from work and pick up a new relay.

Can any of you tell me anything about these relays? I have heard of fuel pump relays going bad, but any info is goodness.

On my '97, I have 3 relays on the firewall in the engine compartment.
Is the unit you're talking about in this area?

I also have two or three behind the cover in the glove box.

If so, try swapping them out with each other if they are similar types, and see if the problem moves with the relays.

As far as stating earlier they either work or don't work, not necessarily. It could be a short or weak connection in the coil, which when energized, either opens or closes the relay (dependant on the type: normally open or normally closed).

On my '97, I have 3 relays on the firewall in the engine compartment.
Is the unit you're talking about in this area?

I also have two or three behind the cover in the glove box.

If so, try swapping them out with each other if they are similar types, and see if the problem moves with the relays.

As far as stating earlier they either work or don't work, not necessarily. It could be a short or weak connection in the coil, which when energized, either opens or closes the relay (dependant on the type: normally open or normally closed).

On the 2000 Jimmy SLE, there is a fuse/relay panel containing a half dozen or so relays and about a dozen fuses that is located above the driver's side wheel well and almost touches the hood when it is closed.

Based upon your comment that there could be sporadic issues, I will see if I can get a new one and keep my fingers crossed.

Well now I am completely stumped. I replaced the Relay with an aftermarket Replacement for $8.00 USD (the dealership wanted $45). This morning when I started the truck, the headlights took about 5 - 10 seconds to light up.

If I have to admit it, I have replaced the Photocell sensor in the dash and the relay for a total of $22. but I don't think I'm anywhere closer to fixing the real problem than when I started.

Two Questions for you electrical experts. 1, can these relays be installed backwards? The pins allow them to be installed into the socket either direction. 2, can the relays be tested?

Two Questions for you electrical experts. 1, can these relays be installed backwards? The pins allow them to be installed into the socket either direction. 2, can the relays be tested?

Does the relay have any markings at all defining the pins and power supply voltage?

Relays would be something like this assuming 4/5 pins- numbers are for explaination as they could be anything, but you get the idea;
pin 1 = coil supply pin
pin 2 = coil ground pin (neutral)
pin 3 = contact 1 common pin
pin 4 = contact 1 normally open pin
pin 5 = contact 1 normall closed pin ( if it's a 2 pole single throw relay)
additional contacts would be numbered similar to 3,4,& 5.


1-----O-----2

3------| |----4
3------|/|----5

1. If installed backwards, most likely you're applying power to the contacts instead of the coil. If the relay is a Normally open contact type, you'd have no headlights. If it's a normally closed contact, you'd be shorting 12 volts (or 5 volts- depending on the supply voltage) to ground, and the relay would probably pop.

2. Yes. If you can determine which 2 contacts are the coil, apply 12 volts (or 5 volts depending on the supply voltage) and ground to those contacts, and listen for a click as you apply power to the coil.
Better yet, if you have aligator clips to apply the power, hook up the ground to the neutral side of the coil, put 1 hand on the relay case, and apply power to the other side (pin) of the coil. You should be able to feel the contact activation at power-up.

I am almost 100% convinced that I am dealing with a bad ground. I have tried 3 different relays in this socket and all 3 did the exact same thing.

Here is the funny part that I cannot explain. Why do the headlights come on and stay on when I lightly tap on the relay? They do not turn off until I turn the engine off. It doesn't matter if I tap on the relay again and again, drive over bumps etc. the lights stay on until I turn the key off.

From Mike's post, I gather that the relay itself is grounded through the socket, but the relay socket panel sits in a plastic box. So, either the relay (and/or the relay socket panel) has a groundwire going out through one of the harnesses or is somehow grounded through the 3 bolts and fender mounted bracket. All I know is that a light tap to the relay turns the lights on if they don't come on when the engine is started.

I am almost 100% convinced that I am dealing with a bad ground. I have tried 3 different relays in this socket and all 3 did the exact same thing.

Here is the funny part that I cannot explain. Why do the headlights come on and stay on when I lightly tap on the relay? .


My next guess would be a faulty crimp on the socket contact(s). Perhaps corrosion, or weak/broken wires at the crimp.
I'm guessing, but I'd lean towards the socket end being bad, as the wires most likely rum from the socket to the EEM where they'd be grounded internally of the EEM. Tapping the relay would indicate your problem lies right at that point. The base is plastic or phenolic, so no ground would be made through the mtg screws.

I'd also guess this is a hard one to diagnose, as those contacts are buried on the bottom side of the socket, and nearly impossible to see.
If you have some electronic spray/cleaner (similar to WD40, but for electronic contact cleaning), give that a try. I used this stuff on my starter when I was having problems with it last year due to salt spray in the winter. No problems since.

My next guess would be a faulty crimp on the socket contact(s). Perhaps corrosion, or weak/broken wires at the crimp.
I'm guessing, but I'd lean towards the socket end being bad, as the wires most likely rum from the socket to the EEM where they'd be grounded internally of the EEM. Tapping the relay would indicate your problem lies right at that point. The base is plastic or phenolic, so no ground would be made through the mtg screws.

I'd also guess this is a hard one to diagnose, as those contacts are buried on the bottom side of the socket, and nearly impossible to see.
If you have some electronic spray/cleaner (similar to WD40, but for electronic contact cleaning), give that a try. I used this stuff on my starter when I was having problems with it last year due to salt spray in the winter. No problems since.
As a matter of fact I do have some electric contact cleaner. I was thinking along the exact same line, a dirty socket. I planned on blowing out the socket with my air hose, but maybe I'll try both.

O.K. here we are again or maybe I should say still. The electrical contact cleaner and air hose did not help. I am reasonably sure now that I have a loose wire or connection somewhere in the under side of the Fuse/Relay panel that is mounted to the driver's side wheel well inside of the engine compartment. The panel appears to sit inside of a plastic box. My problem is, I can't seem to find a way to get to the underneath side of the relay panel where the connections are.

Anyone have any ideas how to get inside of the panel?

You are not alone...I also own a 2000 GMC Jimmy the exception is that the lights come on when I start the truck BUT as you drive it the lights switch from low lights to highlights as you tap along any small bumps in the road. When it switches to the highlights you end up with NO lights at all. This little problem makes for intresting night time driving. Sometimes the lights are totally fine and you can get from point A to B with zero incident. Other time the entire time you are driving it feel like your in a disco club with strobing lights. HELP!!!! Anyone have an answer to this riddle?

You are not alone...I also own a 2000 GMC Jimmy the exception is that the lights come on when I start the truck BUT as you drive it the lights switch from low lights to highlights as you tap along any small bumps in the road. When it switches to the highlights you end up with NO lights at all. This little problem makes for intresting night time driving. Sometimes the lights are totally fine and you can get from point A to B with zero incident. Other time the entire time you are driving it feel like your in a disco club with strobing lights. HELP!!!! Anyone have an answer to this riddle?
Here is all I have been able to come up with. The large Fuse/Relay Panel that sits on the driver's fender wall has sockets that the prongs of the various relays and fuses push down into. The only thing that makes any sense is that the female clips inside of these sockets are either burnt, corroded, or have simply lost their pinch, resulting in a bad contact between the prong on the relay and the socket. I say this because the slightest tap on the headlamp relay turns the headlights on when they don't come on automatically.

I have tried spraying contact cleaner into these sockets as well as crimping the wires goinging into the connectors on the underneath side of the panel. The contact cleaner seemed to help a little, but nothing so far has fixed the problem.

I was thinking about flattening a piece of solid copper wire into 4 thin strips, bending them into an "L" shape and inserting these copper strips into the 4 socket holes in the panel, then installing the headlamp relay into the socket along side of the copper strips to see if this might make a better contact, but I haven't had the time as yet.

Well here we are still or again or whatever. Over a year now and I still am stumped. I had a long repreve (8 months or so) with no issues. But the beast has reared its ugly head again. Once again, I sporadically have no head lights and almost always will turn on instantly when I lightly tap on the Headlamp Relay. Once they Headlights do come on, they stay on until I turn off the ignition with the key.

But the other day when this was happening, I noticed something else which seems to me to be significant. I drove around for quite a while during daylight hours and noticed that the headlights would not turn on even when the photocell was covered up or in the shade. So when I got home, I opened the hood and removed the cover to the Fuse/Relay box and found that the Headlamp Relay was HOT. I don't mean warm, it was hot to the touch, and thumping the relay didn't turn the lights on. I swapped the Headlamp Relay with the Relay for the rear windshield defogger and the headlights came on instantly. I switched them back and put the hot one (which had cooled) back in and the head lights again came on instantly again. I had previously checked and re-crimped all of the wire connectors going to the Headlamp relay, so I'm hoping someone might have seen this issue and can steer me in the right direction.

Rick
If relay heating up it has a over load on that circuit.
It might be a good idea to get a amp meter on the headlight circuits and watch for any heavy amp draws.

Also wiggle wires around when checking it.

This is sounding more like a crummy movie with a possible good ending. I found something kinda funny. On the left side of the dash panel, just below the air vent is a little mini panel with the head light switch on it. Just below the switch is a button marked Dome Override. If you push that button twice, the headlights will go out, push it twice more and the head lights come back on. I pushed this button a couple of weeks ago when my head lights were winking out, the head lights came on and they haven't acted up since.

Any thoughts? I am not foolish enough to get my hopes up, but I will keep my fingers crossed.

AND SO IT ENDS! THANKS TO OLD MASTER, WHO IS A MAN ABOVE MEN, AND HAS THE PATIENCE OF A SAINT. THE PROBLEM IS SOLVED.

After Pouring over the schematics and spending a week exchanging e-mails, Old Master (from 2000 miles away) and I, fixed the problem.

The culprit was a burnt wire terminal in the underside of the Fuse Block that sits on the fender well above the driver's front tire. This Wire was a ground wire dedicated and exclusive to the headlight circuit. It cost nothing to fix. All I had to do was sand the burnt clip clean with a piece of Sand paper and re-attached the clip.

Amen - And I can't even think about how I can ever re-pay OM for his help and guidance.

Awww shucks, twas nothin' Thanks for the kind words, glad I could help. All I did was tell you what wire had a problem. You tracked it down like a blood hound and found it, good job!

Reading through the thread, you mentioned pushing the dome override button twice and the lights went out, twice again and they came back on...... normal operation, Rick. When you start the vehicle and put it in gear, the Daytime Running Lights, (DRL's) automatically turn on the high beam filaments at a reduced voltage. Pushing the dome override twice shuts them off, (should be accompanied with a "ding" from the door chime) twice again turns them back on. If you push it just once, the dome lights will not come on when you open a door.

All I did was tell you what wire had a problem.

Naw, OM you are too humble.

You not only told me what wire had a problem,

You sent me the schematic.

You told me that is was a Yellow wire,

Specifically, a Yellow Ground wire,

And the terminal number it was connected to,

You told me where to look for it, and how to fix it.

All from 2000 miles away.

It took a while to get there, but once I did, BINGO, it was just like you said.

So from now on guys, if Old Master tells you the Moon is made of Green Cheese, just go get the Rye Bread and the Mustard and enjoy the lunch!

Thanks Again Old Master for all your help and guidance.

Hi I'm having the exact same problems with my 2000 blazer. I was wondering if you could let me in on the secret too haha. Thanks in advanced

Headlamp circuitry is quite complex on these vehicles. Several things can control the bulbs: headlamp switch, flash to pass, autolamp, dimmer switch, and daytime running lights, and they are ultimately controlled by the BCM. The headlamps are independently fused, and use an isolated ground circuit that runs through the multifunction switch. Schematics change from year to year, and it makes a difference whether it's ZR2 or not, on the same model year vehicle!

Provided yours is NOT a ZR2, and you're having the exact same problem, with the same exact year of vehicle, Rick can explain how he got to the buss bar to fix it. It involves partially removing the underhood fuse panel. It may or may not be the problem with yours. Let us know if you need help, but be prepared for a lengthy diagnostic procedure. You'll need a basic knowledge of DC circuits, a good quality DVOM, know how to use and understand it, and lots of patience;)

I'm having a similar problem with my 2000 sle. However, it's only the right low and high beam that won't come on. The yellow light (parking or caution?) works fine. I changed the bulb and it still doesn't work. I switched the fuse for the left headlight with the right and it's not the fuse. I have a feeling it's a wire that has come loose. Could you supply me with those directions to check for a loose connection? Thanks

old_master and Rick Norwood, I am having the same exact issues with the headlights on my 1999 gmc jimmy. Can i get the information on the yellow wire. Is it the yellow with black stripe? It really pisses other drivers off when you hace to use the brights all the time. I really need to get them fixed asap. thanks for any help you can provide.

Hello to all:

I am having similar headlight issues. Instead of starting a new thread I thought I'd try adding to this one:

I have an electrical issue with my 2001 GMC Sonoma truck, 2WD 4 cyl 2.2L. My headlights refuse to turn on, both low-beam and high beam. I have checked all the fuses and none are blown. I've found the headlight power relay in the fuse box, and here's the weird thing: If I have the headlight switch turned off, I can feel that relay click when I flash the high-beam switch (but the lights still do not come on, and the dashboard indicator for high beams won't light-up either). If I turn the headlight switch to the "on" position, the aforementioned relay does nothing when trying to once again to flash the high beams. WTF....Also, where exactly is the ground connection for the headlights?

I REALLY hope it's not an issue with the darn turn-signal switch I just replaced that effing thing last year and it was an absolute NIGHTMARE doing so. Thanks in advance for any help! :iceslolan

Hi old master I am having the same problem Rick was having he is not alone every problem he was having with his headlights is describing my problem the relay being hot and all my truck is a 1999 ZR2 Sonoma if you could help me find what ground wire i need to search for under the fuse block I have been suffering this carnage for the last two years throwing parts at it and spent countless hours online researching what a blessing to run across Ricks problem and this forum any help would be great thanks

Ken, it is much easier for us to help you, if you tell us EXACTLY what your problem is, rather than jump on an old post saying it's similar to another problem......

Are you having a problem with your Auto headlights? Do they work manually? Problem with hi's or lo's, or both?

Have you tried swapping a relay? What is the name of this relay that is hot? There are 3 relays involved in this setup.....

Good morning its the DRL Relay thats screaming hot the DRL low beam quits working it wont even come on with the headlight switch High beam works fine if you tap on the relay the low beam come back on I replaced the relay a month ago hope this helps

Don't mean to beat a old horse but what Rick was explaining is exactly whats going on with my headlights

I have replaced the complete UEC on two S10/Blazer vehicles due to rogue problems like this. Finding one in good condition in a wrecking yard is key to resolving the problem. Around here the spray from wet springs, humid summers, and winter road "seasoning" takes its toll. A little corrosion in the bussing and sockets within the UEC goes a long way toward creating these problems.

http://www.wwdsltd.com/files/BlazerUEC.jpg

I have replaced the complete UEC on two S10/Blazer vehicles due to rogue problems like this. Finding one in good condition in a wrecking yard is key to resolving the problem. Around here the spray from wet springs, humid summers, and winter road "seasoning" takes its toll. A little corrosion in the bussing and sockets within the UEC goes a long way toward creating these problems.

http://www.wwdsltd.com/files/BlazerUEC.jpg

Thank you for the information that's where i'll start the search, the highway districts in Idaho use deicer during the winter months it's a corrosive the streets are covered with it. I'm on my way out to unbolt it and look underneath I'll let you know