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2007 Chevrolet Silverado Classic HVAC Blower and Other Problems

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My 2007 Chevrolet Silverado classic LT pickup truck has recently thrown me something of a curveball with an electrical problem it had a few days ago.


I was on my way back home when I noticed that the Engine Hours display in the DIC reset itself to zero (it was reading around 2742 engine hours). I thought that was odd, but nothing else went obviously wrong at the time.


It got worse in time. After making another stop and starting the truck up again, the ABS and brake fault lights came on sporadically, followed by lots of warning chimes. I could find nothing wrong with the brakes. I also noticed that the Engine Hours counter had reset itself to zero once again.


I drove a little while more, with the brake and ABS warning lights flickering and chiming away.


After another stop, the Engine Hours counter had regained its previous memory (relative to the point where it first reset, not the correct value). It has held that information ever since.


Not long after all of this, I noticed that the first four blower fan speeds were missing. I also noticed that I could provoke the whole ABS/brake warning light and chime episodes by toggling the fan switch between the highest setting and any of the lower ones. I later learned that when going down the highway, this would cause the cruise control to shut off (and lose its memory of the previously set speed).


I checked all of the fuses that seemed relevant and found none of them blown. I went on to check all other fuses and still didn't find any that were blown.


So I wondered if maybe the blower resistor pack (and its protective diodes) had failed, thus possibly allowing back-EMF "spiking" of the electrical system and causing both the engine hours counter to reset and the brake/ABS warning lights to misbehave.


I'm apparently not that lucky. Replacing the resistor pack changed nothing.


Other observations:

1. I haven't tested for power at the resistor pack terminals while operating the fan switch. I plan to do this soon as I find my multimeter.

2. The battery terminals are good and tight (first thing I ever checked--the 2003 S10 I used to have loved to go batty in similar ways if the battery terminals were not cranked down to within an inch of their life).

3. Though it seems to work just fine in every way, the battery is an ACDelco Freedom type and might well be original to the truck.

4. With the blower fan shut completely off, the chimes and lights do not misbehave.

5. I haven't looked to see if all grounds are tight. I'm not sure where the ground for the in-cab electrical stuff actually is, and it's been raining so much that I haven't cared to look.

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