Rad Fans run with no key on cold engine

[wifes_truck]

OK, 5:30 pm......(sunday)

Took the complete PCM out of the truck and minutely examined the plugs. to my surprise there actually was a small amount of moisture in the bottom of the blue side and on the bottom pins. however if lead to believe that bottom pin 80 is the culprit, it was clean looking and dry. the 2 on the opposite side were what looked to be a small drop of water.

The green side was super clean and dry after popping off the green bottom cover. so I took wife's hair drier out there and placed it on low heat low blow for about 45 minutes to make sure it was dry. Sprayed the connections out with a can of (radioshack) (remember that place) contact electrical spray. then moved the pins around and placed blow drier back under for another 15 minutes.

while that was drying, i took the 4 bolts off the PCM to look under the cover, looked dry and clean, but not wanting to take any more chances I placed a plastic cover over it and stuck hair drier in there for about 10 minutes to make sure there was no excess moisture. I could have pried open the circuit board that was there after the cover came off, but, back to the not broke don't fix it thing kicked and I left it alone to be safe.

Bolted it all up and now it is back to a wait and see what happens over next few hours.

cheers and I really don't know what next if it turns back on.

cheers and thanks for the support.

 

[Tonyrodz]

OK, 5:30 pm......(sunday)

Took the complete PCM out of the truck and minutely examined the plugs. to my surprise there actually was a small amount of moisture in the bottom of the blue side and on the bottom pins. however if lead to believe that bottom pin 80 is the culprit, it was clean looking and dry. the 2 on the opposite side were what looked to be a small drop of water.

The green side was super clean and dry after popping off the green bottom cover. so I took wife's hair drier out there and placed it on low heat low blow for about 45 minutes to make sure it was dry. Sprayed the connections out with a can of (radioshack) (remember that place) contact electrical spray. then moved the pins around and placed blow drier back under for another 15 minutes.

while that was drying, i took the 4 bolts off the PCM to look under the cover, looked dry and clean, but not wanting to take any more chances I placed a plastic cover over it and stuck hair drier in there for about 10 minutes to make sure there was no excess moisture. I could have pried open the circuit board that was there after the cover came off, but, back to the not broke don't fix it thing kicked and I left it alone to be safe.

Bolted it all up and now it is back to a wait and see what happens over next few hours.

cheers and I really don't know what next if it turns back on.

cheers and thanks for the support.

I hope it works out.

 

[ferrelbirdjr408]

I'll get you a picture of the wiring harness from my 2001 Chevy Suburban if that will help I so hope it does.

Sent from my SM-T580 using Tapatalk

 

[Doubeleive]

I'm thinking outside the box a little bit here... But could the fan motor itself have an internal failure that is causing a short?

no, internal fan failure would result in melted wiring or blown fuses

 

[OR VietVet]

no, internal fan failure would result in melted wiring or blown fuses

Exactly. The fans do not have power all the time that could contribute to a problem. The problem is getting power to them when not needed and also having the ground to complete a circuit that turns them on.

 

[wifes_truck]

OK, ... I was holding out before I wrote this. It has been roughly 28 hours now since I finished that PCM operation. The Tahoe has been out and about driven today, and warmed up and now cold again for last 4 hours. As of this writing, the report is a positive NO FANS are running with a cold engine and no keys in the ignition.

Ron, pass over that ketchup bottle and I will smother those words and spoon right into that bowl of "i told you so's"

If anyone ever gets this problem and needs the answer of what to try first....

1- take out battery, 2- open the plastic holder carefully for the PCM box 3- take the 2 bolts holding the wire harness into the PCM off and examine those closely. and by close I mean any moisture will drive you crazy. take off the blue holders and inspect the pins. It is a bit of a pain as the wires are short.

Then when you are satisfied that that area is completely dry, and the problem continues.... try all other logical steps in trouble shooting..... (good luck to you and i hope you have patients)

I was fooled into thinking they were OK, when the slightest drop in there played havoc.

Or this is what I am hoping has fixed this @#$#@!@ problem.

Thanks for all your trying and suggestions and support on helping me sound off during this frustrating fix.

cheers and if we ever meet, beers are on me

 

[OR VietVet]

I truly truly hope this is a fix. In colder weather the moisture does not evaporate out like in warmer weather. It can even freeze and then melt and stay in there. The shake you did earlier likely just moved the moisture and gave you false hope. The area that moisture was in could not let that moisture out. I dealt with problems similar to this in KC, Mo. and I knew a guy that was a tech at a dealership and his tool box was a carry around, like a bait and tackle box, and he literally wore a long white set of coveralls because he did not get dirty. This type of work was his specialty. He would dig till he found the problem and was very good at it. He told me once, "Don't leave a stone unturned and don't assume". That is why I was saying to you to get in there and unplug and inspect, literally with a magnifying glass. I don't know and neither do you yet if the problem is solved or if that moisture was the culprit but I damn sure hope it was. Look at all the members here that chimed in to help. You may have been ready to give up but your labor is free to us and we wanted you to find it. I truly hope you did.

I don't know how close you are to Oregon, but I will drink that beer with you and your wife if this is a fix and you are in the area. You will be my guest at my American Legion post. Good times!!

By the way, has it ever gone 28 hours with no problems since ANY fix has been attempted?

 

[wifes_truck]

Hi Ron,

Yes I wasn't going to give up ... still had plan "B" if needed. but I was so fooled into believing that it was clean the first time I had it apart, that I was done with that section. The killer was the "how" it waited to turn back on after being off. any logical thinking would have one believing that the short should happen right away when it is connected again. not wait 4 hours later ... head scratch .... electrical gremlins are the worst.

Yes Oregon not that far, but until the border re-opens no road trips in any future that is for sure. lol cheers and thanks again

 

[wifes_truck]

ron, this just reminded me of a different problem when you said leave no stone un-turned... we have a 78 pinto that we rescued and rebuilt. the heater fan stopped running a few years back, and being a summer car didn't really care much. then started driving it later into the fall and decided that maybe I should look into the fan. So glass fuse looked great. decided that maybe the connecting rod/cable was dislodged for the controller, took it all apart and looked.

nope 100% in tact. hmmmm not much can go wrong here....

"light bulb moment" decided to pull the glass fuse out of the holder to look more deeper.... held the 2 metal ends in both hands and slightly pulled, the glass opened and showed the problem.... the filament was burned at the end where you can not see it where it joins the metal tube bit. fuse in the fuse box looked perfect .... cheers

 

[OR VietVet]

Seen the glass fuse problem many many times. Again, like my friend said, "Don't assume". What looks good thru the glass can look completely different when removed and checked for continuity. He always said to unplug and look for the problem like you absolutely know it is there. The fact that you were there and shook it and the problem went away for a period of time meant to me, the problem is in that small area and must be inspected thoroughly. Don't assume anything. If it is fixed, fine. But if comes back, I am still convinced we are on the right track.

I am not going to assume the Tahoe is fixed till a few days go by with no problems. Watch this rig. Monitor it. Assume it is not fixed till IT IS! I have a 2005 Tahoe Z71 and I want this to be a fix because you never know when I may run across the same thing. I love my rig and I know your wife loves this rig as well when is working as it should. The beers and food can wait. The repair can't.