OT: 2004 Envoy Wiring Diagram - Headlights

[Paul Alciatore]

I have a problem with the headlights on my 2004 GMC Envoy XL. Sometimes they work and sometimes not. I have already changed the relays.

I need to find a wiring diagram for the headlight circuit so I can troubleshoot this. I looked on-line and everything there looks like a scam of some type or another. Does anyone have a good, on-line place to look for this?

[Captain K]

Probably need to buy one of the aftermarket manuals. Chilton or Haynes.

[Joe Rogers]

Or find a GM dealership with a friendly shop foreman to print out the schematic. All service info now is on line and accessed from a computer station. Techs don’t lug books to the vehicle any more, just a handful of printed pages.
That said I seem to remember there were lots of overheated connections at the bulbs causing similar issues.
Joe

[J Tiers]

Probably need to buy one of the aftermarket manuals. Chilton or Haynes.

I have had Chilton or Haynes manuals for several vehicles.

I have NO IDEA why I still bother to buy them. Essentially, they have been utterly useless for 90% of what I needed a manual for.

The problem is that they are very generic, they have ONE manual that attempts to cover several years and many sub-models, options, etc, but they have lacked useful information covering differences between sub-models, leaving the user guessing. As for options, just forget it, if it wasn't on the model they looked at, it ain't in there, typically.

The very worst portions of the manuals have been the wiring diagrams. They have varied from incomplete to dead wrong. And, if there is anything I can make sense of, it is wiring diagrams, I am very used to even fairly weird ones, and can "fill in the blanks" when info is unclear, etc.

To be fair, even the auto manufacturers have problems. Just the user manual for the Ranger has many errors, inconsistencies, and portions that are flat wrong. For instance, the fuel capacity is listed with at least 3 different numbers, differing by a couple of gallons, yet there is one basic version of the truck with just body options and accessories. The factory maintenance manual is probably the same. I've had factory maintenance manuals for some of my vehicles, and while they were WAY better than the Haynes, etc, they did often have problems when it came to sub-models and options.

But the Chilton/Haynes manuals are far worse. I still buy them, thinking they must be better than nothing. But when I go to do any work, it still ends up being almost the same as if I did not have the manual at all.

[Sparky_NY]

One of the autoparts chains has schematics on their website. Don't remember which one, Advance or Autozone? I have used that resource many times.

https://www.autozone.com/diy/repair-guides/wiring-diagrams

[DS_park]

Paul I feel your pain on trying to find anything online these days without tripping over a pay us money for.....

I did a google image search on 2004 GMC Envoy headlight diagram. One click enlarges the image and you can right click over it, copy image, and paste into a word processor document (set the doc to landscape first). Unfortunately, it looks like everything (headlight control switch) goes into a computer module (body control module?) which then controls the relays you mentioned.

Sources for diagrams:
Check your local library for books or online access to repair manuals. Copy print copy print.
Someone mentioned autozone above, worth a try.
Online used book stores sometimes have manuals for sale at a reasonable price.
In the past I have signed up for a 1 year subscription to Mitchel Online and then printed and or saved everything I felt useful for future use.

Good luck.

Currently chasing a blower motor speed control issue myself in a 2005 chev that is either the dash control, motor control board or the body control computer. No direct connection, they all talk to each other via computer bus.

[Willy]

Some very good advice already, especially the point of not wasting time and money on a Chilton or Haynes manual, they're cheap for a reason!

Is it the low beams you are having an issue with or both Hi and Lo?

I've run into similar issues on not just Envoy but other GM brands as well, usually associated to high resistance in the power distribution box on buss bars, and or dimmer switch terminals in the power distribution box, etc. Check ALL terminations that affect the headlight circuits there. This issue initially manifests itself as an intermittent problem and usually gets worse with time.

In lieu of a proper factory shop manual one can always use the old fashioned method of tracing each circuit with a continuity tester or ohm meter. I realize this takes time but it will also allow you to ensure that you don't have any bad junctions or high resistance at multi-pin connectors. Take each one apart and reconnect them and then verify they are sound with and ohm meter.

[deltap]

When I was having trouble with a dodge truck I was able to find enthusiast forum that had link to factory manuals. It was a huge file and required a bit of study to be able to use. You should search the forum for your specific problem. If it's a common problem someone will have already tackled it. Take advice with grain of salt. Some are excellent and others are cowboys. Intermittents are harder than it don't work. Always check grounds first. They are numerous. Check for corrosion on underhood connectors especially large ones to computers etc.

[Guido]

Pretty interesting reading regarding the “right to repair laws” which John Deere, Caterpillar and other big boys are now backing away from. ‘Guarantees and warranties are void if’n you use non certificated/non factory trained repairman or rogue repair parts’.

[sarge41]

Paul: I remember some years back , I consulted some Mitchell's books at a local library that were just auto electrical schematic's. Good luck.

Sarge41

On edit: Paul, Out of curiosity, I googled Mitchells and they have a DIY program that will allow you to subscribe for 31 days (one vehicle) for $19.95. I don't know if you are interested in something like this or not.

[reggie_obe]

I have a problem with the headlights on my 2004 GMC Envoy XL. Sometimes they work and sometimes not. I have already changed the relays.

I need to find a wiring diagram for the headlight circuit so I can troubleshoot this. I looked on-line and everything there looks like a scam of some type or another. Does anyone have a good, on-line place to look for this?

Both low beam and high beams out?
Does it have daylight driving lights? Are they working?
What relays did you replace?

[tom_d]

I see that both the Haynes and Chilton books are available through RockAuto. Both claim to have wiring diagrams. Not sure how thorough these books are.

Ebay shows a few vendors peddling the factory service manual available in disc form for not much money. Might be worth the risk. Publication prices come way down when yo get things in digital form. I've done this type of purchase for a few cars over the years and have been successful. Of course with everything automotive, your mileage may vary.

Intermittent problem with the lights? I'm wondering about a circuit breaker that might be on the way out, or is there one in the line with an auto reset that's doing its job?

[Paul Alciatore]

It is the low beams that are intermittent. Sometimes they work and other times they do not. The high beams work perfectly: both for full on and to flash them.

I replaced the relays that operate the low and the high beam lights. I am not really sure if it has daylight light operation: I need to check the user manual.

Since it is an intermittent situation, sometimes they work and other times they do not, I need to do some kind of troubleshooting. What I hope to do is use a temporary circuit that will have an indicator (LED) that shows when the proper Voltage is applied to the lights and that can also use a switch to positively turn them on when the $700 module does not. I figure a simple, double throw toggle will do that. I am going to run a cable from under the hood to the driver's position. Cut the wire to the low beam connection at the lights and drive it until I detect a failure. Or not. This can take quite a while, but I need to do something.

I would actually pay the dealer to change out that $700 module IF they would just guarantee that it WILL FIX the problem. But they will not do that. They will replace it and if the module goes bad in 30 days that is guaranteed. But not that it will actually fix the problem. Typical of all the dealer and most of the private shops. No real guarantee on actually determining where the problem actually is. If they guess wrong, the customer just pays and pays and pays while they change one part after another until they get lucky. This could just be a loose wire, but they change the most expensive part first.

And I am NOT crazy in asking for this. I spent over 45 years in electronic maintenance and I had to find the actual problems. I can do it here too, but I would like to have a circuit diagram to work with. They could do it, but they won't.

Diagram or no diagram, I am jumping into this Sunday. It will just take longer without it.

Both low beam and high beams out?
Does it have daylight driving lights? Are they working?
What relays did you replace?

[JRouche]

I have a problem with the headlights on my 2004 GMC Envoy XL. Sometimes they work and sometimes not. I have already changed the relays.

I need to find a wiring diagram for the headlight circuit so I can troubleshoot this. I looked on-line and everything there looks like a scam of some type or another. Does anyone have a good, on-line place to look for this?

I dont know. Kinda weird we have an electrical guru (My Words) asking for car electrical stuffsss.

No kiding! The cars are full of miles of wires and computers these days..

Used to be one computer freaked people out. We have between 5-20 seperat computers now. I rippied my car apart, they are everywhere.

Airbags, engine, trans, lighting, cameras, radar, sonar. and more. I did put the car back together, what! I am not a barbarian. Good as new, . JR

[reggie_obe]

It is the low beams that are intermittent. Sometimes they work and other times they do not. The high beams work perfectly: both for full on and to flash them.

I replaced the relays that operate the low and the high beam lights. I am not really sure if it has daylight light operation: I need to check the user manual.

Since it is an intermittent situation, sometimes they work and other times they do not, I need to do some kind of troubleshooting. What I hope to do is use a temporary circuit that will have an indicator (LED) that shows when the proper Voltage is applied to the lights and that can also use a switch to positively turn them on when the $700 module does not. I figure a simple, double throw toggle will do that. I am going to run a cable from under the hood to the driver's position. Cut the wire to the low beam connection at the lights and drive it until I detect a failure. Or not. This can take quite a while, but I need to do something.

I would actually pay the dealer to change out that $700 module IF they would just guarantee that it WILL FIX the problem. But they will not do that. They will replace it and if the module goes bad in 30 days that is guaranteed. But not that it will actually fix the problem. Typical of all the dealer and most of the private shops. No real guarantee on actually determining where the problem actually is. If they guess wrong, the customer just pays and pays and pays while they change one part after another until they get lucky. This could just be a loose wire, but they change the most expensive part first.

And I am NOT crazy in asking for this. I spent over 45 years in electronic maintenance and I had to find the actual problems. I can do it here too, but I would like to have a circuit diagram to work with. They could do it, but they won't.

Diagram or no diagram, I am jumping into this Sunday. It will just take longer without it.

Lots of YouToob videos for Envoy and Trailblazer headlight issues.
Was the relay you changed the one on the "customization" board in cab? Seems most faults point to the SSR under the hood. See this vid: https://youtu.be/6Diuvxs9X_Y?t=45
and https://www.youtube.com/watch?v=ViJzaedBpgs