Battery not charging

A thank you to all in advance. So, I'm driving home from work in my 2004 Yukon XL Denali when, out of the clear blue, it goes into LHM. This vehicle has 240,000 miles on the odometer and I have owned it since new. The only other time LHM mode has happened was last summer when I was driving home from Texas. A new throttle body was installed and we were on our way.

Fast forward to last week. I managed to get her home, put the scanner on it, and found that it indicated a faulty TPS. Kind of odd for a virtually new throttle body, but I am sure not unheard of. I installed a new TPS and life has been miserable ever since.

No supply coming from the alternator, a couple of blown fuses, and total confusion on my part. I picked up and installed a new alternator, figuring that the original had 240K on it. By the way, new alternator, not reman. Replaced the fuses, fired her up, and...……...same result. Now I have learned that the PCM controls the alternator so I'm guessing that there is a problem with the PCM.

Can the PCM be removed, taken to a shop, and re-flashed, or am I doomed to having the vehicle towed to a shop? As a career aircraft mechanic, not much challenges me, but I am more than happy to admit defeat on this one. Help, please!

What code did you get? Lots of folks with limp home mode issues. Check the wire harness for the TPS, they apparently get brittle, check all the grounds Is that seems to have been a problem for many as well. Others more knowledgeable out there though and hopefully chime in.

afpj said:

What code did you get? Lots of folks with limp home mode issues. Check the wire harness for the TPS, they apparently get brittle, check all the grounds Is that seems to have been a problem for many as well. Others more knowledgeable out there though and hopefully chime in.

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I am at work right now with no access to the scan tool. However, I did check the ground and some of the other leads. My question would be this.....would the replacement of the tps cause this to happen?

I’d go after the wiring to the tps and look for brittle or exposed wire. It doesn’t take much to set this chain of events off. The grounds and cables are a common issue for older rigs like ours. Post the code when you can. Do you have a Tech2?

Big Mama said:

I’d go after the wiring to the tps and look for brittle or exposed wire. It doesn’t take much to set this chain of events off. The grounds and cables are a common issue for older rigs like ours. Post the code when you can. Do you have a Tech2?

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No, I use an Autel MD808. As to the wiring, it's an amazing thing. I used to be able to open the hood and see what GM knit together when they built this truck. Now, however, with each and every part that I replace, I notice the wiring loom disintegrating. All you have to do is flex the cable housing and it crumbles like chalk. Now I look into the engine bay and see all of the electrical tape that I have used to patch the loom back together. I appreciate your help and I will get back into the loom and take a look. By the way, the grounds all look good. Thanks, again.

My looms are the same way. I had some red loom from a street truck I built so now I have some red and some black.

Now I am more suspicious of the tps harness. Neither of the two blown fuses I found appear to be affiliated with the tps, but anything is possible at this point. Gonna have to see what damage I might have done.

I should have guessed that the TPS harness was the issue, at least the starting point. I finally managed to get back under the hood, removed all of the covers and lit the engine bay to be able to see better. Lo and behold, upon removing the TPS plug and peeling back some of the loom, I found the yellow lead had been ground through and the wire was broken. Repaired the wire, figuring that was it.

Hooked up the scan tool, fired up the Denali and, sadly, had the battery light came back on. Shut off the engine, gave it a few seconds, and fired her up. No battery light, DIC was clear, but only showing battery voltage on the voltmeter. More importantly, code P0622 (generator F terminal) displayed on the scanner. Started the car a couple of times and have a continuing battery light and "battery not charging" on the DIS. Frustrating to say the least. I'm going to wiggle a couple of the connectors and see if there is a change.

Just wanted to give you guys an update. Thanks for the responses.

There is a TSB for the TPS harness, sometimes the wire breaks inside but the plastic shield is intact. You can check by pulling on each wire and if one stretches that means the wire is broken inside.

FOUND IT! I'm really not sure how this could have been a part of the initial problem, but perhaps high resistance was the issue. While moving some of the electrical fittings around, I twisted the lead that exits the alternator and goes to the red battery block. It sparked and burned my fingers. I shut the engine off, pulled that lead, and discovered that, upon pulling back a couple of inches of insulation, about 1/2 of the wire had corroded away. Short of measuring resistance at the terminals, I doubt if this would have ever been seen. Burning my fingers exposed the problem. I had a short battery cable in my toolbox that I was able to use in place of the corroded piece. Bingo, no lights, everything charging normally, and the voltmeter indicating the proper voltage.

Thank you to all of you for your much appreciated help. These forums have proven to be a boon to those of us who still enjoy working on our own vehicles.