Electrical - where to begin

[Moosemoon]

Good baseline to start from. At least you won't be chasing all other systems forever, only to find out problems were chassis grounds!

I am sure the expert electrical gurus will get you figured out pretty quickly.

Thanks I hope so.

 

[S33k3r]

I'm SO sorry I am getting to this late, but it sounds like you are experiencing an alternator failure. That is one of the few things that would cause issues with all these electrical systems at once. The alternative, of course, is that something the mechanic did or it sitting for so long took out multiple systems. But the fact no one can find anything wrong leads me to look at the alternator.

Additionally, we had some issues with a bunch of subsystems on my Wife's Suburban; it turned out the cables going to the ECM were rusted; they were either broken or the resistance was so high current wasn't flowing. But she had driven through some high water on a 1000 year rain day.

I wish you were down here -- I could suggest a GOOD, HONEST mechanic you could take it to.

***** EDIT: If you get the chance, please share some pictures of your rig.

 

[Doubeleive]

I'm SO sorry I am getting to this late, but it sounds like you are experiencing an alternator failure. That is one of the few things that would cause issues with all these electrical systems at once. The alternative, of course, is that something the mechanic did or it sitting for so long took out multiple systems. But the fact no one can find anything wrong leads me to look at the alternator.

Additionally, we had some issues with a bunch of subsystems on my Wife's Suburban; it turned out the cables going to the ECM were rusted; they were either broken or the resistance was so high current wasn't flowing. But she had driven through some high water on a 1000 year rain day.

I wish you were down here -- I could suggest a GOOD, HONEST mechanic you could take it to.

***** EDIT: If you get the chance, please share some pictures of your rig.

if this was the issue there would be a variety pack of codes and issue's and this is simply not the case. there is a airbag code, knock sensor code, and fuel pressure/level issue.
most likely not related to the alternator.
if there was low voltage you would see all kinds of stuff going on or not working period.

 

[S33k3r]

if this was the issue there would be a variety pack of codes and issue's and this is simply not the case. there is a airbag code, knock sensor code, and fuel pressure/level issue.
most likely not related to the alternator.
if there was low voltage you would see all kinds of stuff going on or not working period.

Had this happen with a buddy's Yukon XL 2500. It absolutely was the alternator. This kind of crap CAN happen from a dying alternator. Could also be the power cable running between the alternator and the battery. I've heard of that thing rusting within the insulation and causing issues.

Note that, at least some of the problems CAN be caused by a weak or dying alternator. Because she's had someone else's hands in this vehicle and it sat for 2 years, it is most likely a combination of headaches. But I believe it won't hurt to test the alternator.

 

[Doubeleive]

Had this happen with a buddy's Yukon XL 2500. It absolutely was the alternator. This kind of crap CAN happen from a dying alternator. Could also be the power cable running between the alternator and the battery. I've heard of that thing rusting within the insulation and causing issues.

Note that, at least some of the problems CAN be caused by a weak or dying alternator. Because she's had someone else's hands in this vehicle and it sat for 2 years, it is most likely a combination of headaches. But I believe it won't hurt to test the alternator.

not impossible but normally if this was the case there would be other issue's, certainly could not hurt to verify 13.4v minimum to the battery with engine running.

 

[Baja_Bob]

could not hurt to verify 13.4v minimum to the battery with engine running.

This alternator could put out 13.4v needed, but it actually needs a current test also. Too much or too little current will cause problems to sensitive circuits like these.

 

[Doubeleive]

This alternator could put out 13.4v needed, but it actually needs a current test also. Too much or too little current will cause problems to sensitive circuits like these.

having owned multiple gmt800's for over a decade I have doubts that it is the alternator, certainly cannot hurt to rule it out but I think it's a goose chase.

 

[afpj]

For the alternator idea, it's not enough to check voltage. At this age, cold have rectifier giving out, with some ac ripple getting through intermittently.

 

[S33k3r]

For the alternator idea, it's not enough to check voltage. At this age, cold have rectifier giving out, with some ac ripple getting through intermittently.

Could you please restate that with smaller words? I do not understand your response.

 

[afpj]

As you wish....For the alternator idea, it's not enough to check voltage. At this age, cold have rectifier giving out, with some ac ripple getting through intermittently


Our system is 12 VDC. If any AC voltage/current is let out because the rectifier is failing, the DC rated components behave badly, like all sorts of unrelated codes, potentially (like bad grounds)

 

[Moosemoon]

I'm SO sorry I am getting to this late, but it sounds like you are experiencing an alternator failure. That is one of the few things that would cause issues with all these electrical systems at once. The alternative, of course, is that something the mechanic did or it sitting for so long took out multiple systems. But the fact no one can find anything wrong leads me to look at the alternator.

Additionally, we had some issues with a bunch of subsystems on my Wife's Suburban; it turned out the cables going to the ECM were rusted; they were either broken or the resistance was so high current wasn't flowing. But she had driven through some high water on a 1000 year rain day.

I wish you were down here -- I could suggest a GOOD, HONEST mechanic you could take it to.

***** EDIT: If you get the chance, please share some pictures of your rig.

Thank you for that input. Not something that has been mentioned before. Would there be other alternator symptoms?
It is in the plan today to start checking connections to the PCM, etc.
Yukon was indoors the whole time but it did sit torn apart for some 22 months and not driven for a full 24.
will post pics later today.

 

[Moosemoon]

Had this happen with a buddy's Yukon XL 2500. It absolutely was the alternator. This kind of crap CAN happen from a dying alternator. Could also be the power cable running between the alternator and the battery. I've heard of that thing rusting within the insulation and causing issues.

Note that, at least some of the problems CAN be caused by a weak or dying alternator. Because she's had someone else's hands in this vehicle and it sat for 2 years, it is most likely a combination of headaches. But I believe it won't hurt to test the alternator.

Will absolutely put that on the list for today - check the cable and the volts!
yes there are many other headaches - most seem to have obvious solutions, the codes fixes are not obvious so I really appreciate any and all suggestions

 

[Moosemoon]

For the alternator idea, it's not enough to check voltage. At this age, cold have rectifier giving out, with some ac ripple getting through intermittently.

I think I sorta get what you are saying - but will need to do some reading to totally understand. Additional info?

 

[S33k3r]

Thanks! And thanks for being more specific about my experience with dying alternators too!

 

[Moosemoon]

As you wish....For the alternator idea, it's not enough to check voltage. At this age, cold have rectifier giving out, with some ac ripple getting through intermittently


Our system is 12 VDC. If any AC voltage/current is let out because the rectifier is failing, the DC rated components behave badly, like all sorts of unrelated codes, potentially (like bad grounds)

 

[Moosemoon]

if this was the issue there would be a variety pack of codes and issue's and this is simply not the case. there is a airbag code, knock sensor code, and fuel pressure/level issue.
most likely not related to the alternator.
if there was low voltage you would see all kinds of stuff going on or not working period.

Most all the codes do reference voltage. I have had many other codes come and go for no apparent reason. Checking the alternator can’t hurt right?

 

[S33k3r]

In my opinion, if it were only a ground issue, there would be some consistency to the issues you are facing. There doesn't seem to be any. This leads me to believe it is a positive issue. Also, I have seen similar issues in four other vehicles, one of which was a Crown Victoria (the other three were a 2003 Sierra Denali, a 2004 Silverado 2500, and a 2005 Suburban 2500).

 

[B-train]

This has been a great thread so far. Lots of good info. What was/is the overall condition of your truck as far as corrosion goes? I can't think it would be too bad in ID, unless they do use salt out there.

My speculations are as follows:
1. Corrosion from elements over time. Also, corrosion from natural moisture, especially if it sat for 2 years outside, or on grass or gravel. Vehicles parked on non-solid surfaces are more prone to moisture related corrosion issues from my experience. I'd go over Chassis ground points with a wire brush, coat area with dielectric grease, and reassemble. Use a star washer if provided. Also check the main cables for discoloration and tightness of crimped areas.
2. Modules that died slowly from sitting so long. The steady decline can mess them up
. Or, a jump start from stone-cold dead as well. Have the battery load tested.
3. The alternator idea was something I didn't think of, but I would put down as a relevant idea. You could make sure the battery is fully charged, them remove the power wire from the alternator (tape it up, or put it in a non-conductive covering. Run the vehicle for a short time and see if anything changes. If you have a weak battery, this test won't work well.
4. Do a general inspection of wiring harnesses for pinched areas, worn areas, etc. Being that the trans and motor were gone through, it's a possibility something didn't get put together correctly. Look for proper routing near heat shields, mounting points, etc. Also look at connections to make sure they are in fact "clipped" together properly.

I absolutely HATE electrical gremlins. My hat is off to you for having the gumption to learn and tackle this yourself. Best of luck! Hopefully this brain trust (meant in sincerity) of a group can help you get it figured out. LOL

 

[afpj]

I think I sorta get what you are saying - but will need to do some reading to totally understand. Additional info?

Easy to remove alternator and take it to get bench tested. I believe most retail auto parts stores can do this for free. Not suggesting to get a replacement, yet. Hopefully the tester puts it on a scope or other device rather than just looking at voltage.

 

[Doubeleive]

Most all the codes do reference voltage. I have had many other codes come and go for no apparent reason. Checking the alternator can’t hurt right?

you can pretty much test it yourself by starting it up turn everything on lights, hazard switch, heater full blast, radio, windshield wipers on full speed, defroster. and anything else
then take your meter and see how many volts are at the battery terminals, then also check at the alternator output, it should match what is being sent to the battery or be very close to the same should have no more than 1-2% difference