03 Yukon throwing all kinds of warning lights

[1yesfan]

03 with 160k or so. When it was purchased all was good ran great no check lights, just burned some oil.
Alt and batt died at the same time, replaced them. Ever since I have had check/warning lights coming on. The 4x4 lights would flash like a xmass tree, then get 4x4 fault light, aig bag light warnings, once the trans even went into limp mode, last night when the airbag thing happened the compas light went out, the air bag lights came on in dash and on instrument cluster Every time if you turned the truck off then back on it went away and all was good for days, then something would come back again.
Seems to me I have a gremlin in the works? Main computer? Could I have missed something on the installation of the alternator? I bought the correct for the truck.
Just makes no sense that all these random warning lights for diff systems on the truck go off, then go away and all is good for a time.

 

[shreksbrother]

Hello,

A first suggestion I would make (as would many others on here) is to check your grounds. Heck, even remove them, clean the surfaces and retighten them. They are the cause of many a headache on this forum.

 

[1yesfan]

I had thought about that. Where are they?

 

[cmc76]

i dont have the supporting documentation. But a great sticky would be ground locations with pictures.

 

[1yesfan]

I have googled this ground thing, found some info on the million ground points on the truck. ganna be a weekend thing to just go over it. Just funny, it ran well for a few months, then the batt and alt sh*t on us and these issues pop up time to time. Got to wonder if there is a BCM or ECU going bad.

 

[D is for DENALI]

There's a ground coming from the negative battery cable...follow it to the frame underneath the truck... That's the easy one.

There are 3 ground connections of concern, the one at the back of the engine (near the firewall) connected to the block on the passenger side just below the cylinder head, the one on the back of the engine connected to the back side of cylinder head on the driver's side of the engine, and the grounds on the frame under the drivers side door which is easy to get at but the others are NOT. Start out by removing and cleaning the ground connection on the frame under the drivers door, if you have to use a grinder or equivalent to get good clean metal on the frame then do so. This MIGHT solve the problem but I doubt it will alone but good to do anyways.

Next comes the fun part. The two grounds on the back of the engine are IMPOSSIBLE to get at without removing the intake manifold unless you are some sort of contortionist with very small hands and have x-ray vision and can see through metal. You want to remove the intake to get at them and you want to do this anyways as there is more to this story. The intake gaskets are known to fail causing an intake leak and excessive pinging under acceleration, so while you in the process of getting at the 2 grounds, replace the intake gaskets and you might as well replace the knock sensors (as they may be corroded) and the knock sensor wire harness for good measure while you are in there.

After the intake ducting is removed, the intake is off, etc., etc. The ground on the passenger side of the block is held on by a 13mm bolt, the one on the drivers side is a 15mm (at least it was in my case). This requires you kneel on the upper portion of the radiator support to reach them and is still somewhat of a trick, use some padding to protect your knees.


You will see the ground cable metal strap on the block bolted to the firewall, follow it to the find the mounts on the engine...



Also, remember when doing this work and disconnecting the battery for hours, you will need to do a throttle body "relearn".

Your PCM may have grounding issues: The PCM is located at the front of the drivers side inner fender. Get it out in the open and removed the blue plug, look for the black / white wire in the #1 pin position which is the ground. A few inches from the plug, carefully strip back some of the plastic covering the wire, do not cut the wire! Solder on another wire to this ground, re-cover it well after you have made this connection and run this lead as an additional ground up to the lug on the firewall where the main ground strap from the engine is connected..

Hope this helps you find the issue!!

 

[Chubbs]

I would have returned that alternator and tried another unit. Maybe the battery too at first, if it were possible. It's obviously a charging issue so I would have checked my connections then started returning/ replacing the parts that I bought. After all of that I would be looking at the grounds and voltage output but the simplest/easiest first. I can't remember how many different parts I have bought off the shelf, new in the box that were faulty or compromised. Keep your receipts and return that junk the second you have problems.

 

[JetBlackNali]

Wonder if you have a broken wire or a bent pin on the plug that goes into the alternator?

 

[M1Gunner]

Don't rule out the ignition switch. It may completely coincidental with replacing the alt and batt but the symptoms you're describing could have a root cause being the ignition switch especially with that mileage and if it's original.

Start the vehicle and turn the ac on. Gently jiggle the key in the ignition. Watch for any signs such as the ac button light flickering or going out. Listen for any relays clicking.

 

[1yesfan]

thanks folks, lots to look at.