2005 Tahoe Electrical/BCM Issue

meldmur · October 28, 2018

Hoping someone will have a new suggestion or idea for our problem. We have a 2005 Tahoe 4WD 5.3 that we've had since 2008. It's been a great vehicle and has only needed normal maintenance type repairs until now. About a month ago we noticed the coolant fan would either continue running or it would kick on by itself through the night and kill the battery. My husband changed all the fan relays and even the coolant temp sensor. The high speed fan started kicking on as well, at odd times when it was definitely not overheating or under stress. The battery is a year old and our battery jumper shows it's still good and the alternator holds a charge. Tahoe then started missing bad and generally running real crappy. We took it to a mechanic and he said the ECM was very corroded so he cleaned and sealed it with dielectric grease. It ran perfectly for a week and then the fan started killing the battery again. We ordered a new ECM programmed for our VIN. It's Fall here and cool weather so we just pulled the middle fan relay to keep the fan from running so we could continue to drive it. While we were waiting for the ECM, the dash cluster started acting up intermittently. All gauges would stop working, power door locks stopped, windows locked and the DIC would start cycling through every error message. A day or 2 later it left me stranded at work when it wouldn't start, would turn over and run for a second and then immediately shut off. My husband installed the programmed ECM and we went through the relearn procedure. Tahoe started right up and ran great. Next morning the dash cluster lit nearly every error light and gauges stopped working again. I left the truck sitting for 3 days, not wanting to be left stranded somewhere again. During all this my husband has pulled and checked every fuse and relay and we don't have any blown. There are no obvious ground wire issues. Yesterday we decided to check for a Mega Fuse that I had read some GM trucks have. Couldn't find that fuse anywhere, I guess my 05 doesn't have one. But we realized that the fan had kicked on and killed the battery again. As soon as we attach the battery jumper the fan is running. So new ECM, new fan relays and temp sensor, no blown fuses and no obvious ground wire issues and we still can't get the fan to stop killing the battery and now the intermittent dash cluster issue. Yesterday we took it for a short drive and so far today no dash issues for the moment. We're thinking maybe it's the Body Control Module now. But it seems odd that the ECM and BCM would both go bad at the same time. And I don't think a new BCM is going to help the fan issue at all since it only controls the interior electronics. We plan to take it back to a mechanic or a dealer to see if they also suggest a BCM but not until the dash starts acting up again so they can actually see the issue. Sorry for the super long post but I didn't want to leave anything out. Any other suggestions or ideas at this point would be very welcome!

txab · October 28, 2018

Check and clean ground connections (there are are several). Check Battery cables, not only at connection points, but also internally. They can and do fail.

Have battery load tested first. May only be a year old but can still be having issues

Edited October 28, 2018 by txab

silveradosid · October 29, 2018

check wiring for the a/c high pressure switch for corroded connectors or broken wires that pressure switch will trigger the fan to come on

meldmur · October 30, 2018

Thanks for the replies! I've actually been driving it for 4 days now with no further dash issues. I read somewhere that a total rundown of the battery will sometimes reset all the electronics and I'm thinking maybe that is what has happened. I left it sit for 3 days and then realized the fan had killed the battery again and there's been no issues from the dash since. Fingers crossed anyway! Now we just need to figure out why the fan has a mind of it's own and likes to run in the middle of the night. That's going to be a big problem in the Spring and Summer when the fan will be needed to keep the temp down. I will have the battery load tested just to be sure. And thanks for the tip about the a/c high pressure switch. I'll let you know what we find.

Bcorr12 · August 19, 2022

I know the chances of a reply are slim 4 years later but did you ever solve this issue? The exact sequence of events has been happening to mine and I can’t figure it out. This is the only post I’ve found online that describes what’s been happening.

Bcorr12 · August 19, 2022

I know the chances of a reply are slim 4 years later but did you ever solve this issue? The exact sequence of events has been happening

On 10/30/2018 at 5:30 PM, meldmur said:

Thanks for the replies! I've actually been driving it for 4 days now with no further dash issues. I read somewhere that a total rundown of the battery will sometimes reset all the electronics and I'm thinking maybe that is what has happened. I left it sit for 3 days and then realized the fan had killed the battery again and there's been no issues from the dash since. Fingers crossed anyway! Now we just need to figure out why the fan has a mind of it's own and likes to run in the middle of the night. That's going to be a big problem in the Spring and Summer when the fan will be needed to keep the temp down. I will have the battery load tested just to be sure. And thanks for the tip about the a/c high pressure switch. I'll let you know what we find.

to mine and I can’t figure it out. This is the only post I’ve found online that describes what’s been happening.