'05 Silverado. Fans Come On Shortly After Engine Off. Kill Battery

Raydar · May 16, 2011

As the topic title says, a few seconds after I shut off my engine, the cooling fans kick on. I can only assume that they will keep running forever. I came out to a dead battery this morning. When I hooked up the jumper cables, the fans came back on.

Turning the key on causes the fans to shut off. Turning it off causes the fans to come back on after a few seconds.

I have the schematic and the description. Since there is a delay for the turn-on, it would appear that the PCM is telling this to happen, although I haven't actually measured any voltages or done any other troubleshooting.

Is there anything else that can cause this? (I read that the fans are supposed to shut off after 3 minutes, regardless. Obviously that is not happening.) Is this a common problem? (Since I couldn't find this problem discussed anywhere else, I'm guessing it's not.)

As a last resort, can I pull out relay #1? (It would appear that that's the only relay that's involved in the low speed scenario.) Would I still have at least one fan work in the high speed circuit?

Really don't want to replace a PCM for such foolishness.

The vehicle is an '05 Silverado 1500 crew. 2WD. 5.3.

Any help will be appreciated.

Raydar · May 22, 2011

FWIW, it appears that the battery was the culprit.

When it discharged to 5.5 volts, and then I tried to jump it with a spare battery that was not in a car (Of course there wasn't enough juice) I'm guessing that I got the computer in some sort of a "brain scrambled" state.

Once I got the new battery, and left it disconnected overnight (allowing everything electronic to discharge completely) and reconnected it the next afternoon, everything was fine.

Another clue that points to this is that when I connected the jumper cables, the parking lights (not the DRLs) came on. No switch selection would get them to turn off. They're probably controlled by the BCM, but that was another odd symptom that went away after everything had been allowed to discharge completely.

markw8 · May 23, 2011

Computers and low voltage don't mix. Not much comes on directly from a switch anymore. The switch signals the bcm, pcm etc.

Mark

8.1HD/ALLISON · May 23, 2011

Computers and low voltage don't mix. Not much comes on directly from a switch anymore. The switch signals the bcm, pcm etc.

Mark

+1

Srvelis1 · December 23, 2013

My cooling fan is coming on a couple minutes after I shut the engine down as well. It has ran my battery down twice. Any suggestions? Is it always the battery? How can I check it!

markw8 · December 25, 2013

My cooling fan is coming on a couple minutes after I shut the engine down as well. It has ran my battery down twice. Any suggestions? Is it always the battery? How can I check it!

It's a good place to start. Digging up 2 1/2 year old threads isn't.

Mark