Electrical Gremlins?

drummerdude152002 · January 17, 2021

Having some strange issues with the 03 GMC Yukon SLT of mine.

Last couple of days the wife tells me it's showing a "battery not charging" error on the dash.

Charged it up last night when she got home from work, and had to run some errands today. About the first 10 minutes of driving around the error would display intermittently, until finally it quit, and the gauge was showing a constant 14V to the battery.

Had the guy at O'Reilly test the battery. Tested good. He tested with and without the engine running, both tests showed good, so the alternator, at least for the time being, should be good.

Then, on the way home from our errands, the rear HVAC blower kicked on, even though the dials are all set to off. Tried move the dials around, nothing. Even with the engine off, key out, and driver and passenger doors open, the rear hvac blower was on.

Disconnected the battery about a half hour. Came back out, and as soon as I made the connection (which sparked, telling me there's a current draw) the rear hvac kicked back on.

The HVAC issue may or may not be connected do the battery charging issue. I DID recently replace the rear hvac control module ( https://www.ebay.com/itm/03-06-Yukon-Denali-Escalade-Suburban-Tahoe-HVAC-Rear-Control-Module-15185966/133553680962?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 ).

Anybody have any ideas? I've read some forums about pulling fuses "under the seat" but have no idea what they're talking about. I only know of 2 fuse locations, one under the hood, and one on the driver side panel of the dash.

drummerdude152002 · January 18, 2021

Update:

I disconnected the rear hvac control module (linked above) which SHOULD have turned off the blower (if it was faulty) and the blower still kept blowing. Only after physically disconnecting the harness going to the blower was I able to get it to turn off.

This tells me there's potentially a relay that's stuck closed. Anybody have any idea what relay controls the rear blower and where that fuse box is?

Sharpz · January 18, 2021

how do you know the rear control modual you put in is good? Seems since you recently put that in would be the 1st place I would look. If you spliced wires in make sure you connected everything correctly. I am just guessing here, but I would think if it were a fuse issue, you wouldnt have power at all. If there are not control switches in the back, and only in the front, I would have that control module tested too. It sounds to me you have a short or parasitic draw somewhere, again I would check your work and then test that actual part first, then the front control module 2nd.

drummerdude152002 · January 19, 2021

12 hours ago, Sharpz said:

how do you know the rear control modual you put in is good? Seems since you recently put that in would be the 1st place I would look. If you spliced wires in make sure you connected everything correctly. I am just guessing here, but I would think if it were a fuse issue, you wouldnt have power at all. If there are not control switches in the back, and only in the front, I would have that control module tested too. It sounds to me you have a short or parasitic draw somewhere, again I would check your work and then test that actual part first, then the front control module 2nd.

Part was put in at the end of October and has been working flawlessly ever since. Didn't have to splice anything. All factory harness connection.