Rad Fans run with no key on cold engine

[wifes_truck]

Hi Ron, I was hoping it was fixed. I would eat my words to not have to climb back into that engine compartment again... lol .. i have never seen or heard of anything like this before. Its almost like a Larel and Hardy sketch, or an inquisition of "who's on first". Wife did mention maybe bite the bullet and take the PCM to chevy dealer and see if the PCM is shot and they can reprogram it??? or buy a new one ... she does love the Tahoe ... It does run strong.

Loss for ideas now. I feel your caring ... LOL thanks for the encouragement.

cheers

 

[Tonyrodz]

Hi Ron, I was hoping it was fixed. I would eat my words to not have to climb back into that engine compartment again... lol .. i have never seen or heard of anything like this before. Its almost like a Larel and Hardy sketch, or an inquisition of "who's on first". Wife did mention maybe bite the bullet and take the PCM to chevy dealer and see if the PCM is shot and they can reprogram it??? or buy a new one ... she does love the Tahoe ... It does run strong.

Loss for ideas now. I feel your caring ... LOL thanks for the encouragement.

cheers

Hmmm, I wonder if maybe some moisture and corrosion got to the pcm. It is possible.

 

[OR VietVet]

Hmmm, I wonder if maybe some moisture and corrosion got to the pcm. It is possible.

Like Tony says, There is a real possibility that the PCM is FUBAR on that circuit. Typically the PCM is the last thing to think is bad. It is typically the other parts/items in the circuits that are exposed to real world exposed problems like temp and moisture and salt and such and in this case, that pcm is exposed. I really would be the last person to point at a pcm, but maybe, like the lady says, that damn thing is jinxed.

 

[Tonyrodz]

Like Tony says, There is a real possibility that the PCM is FUBAR on that circuit. Typically the PCM is the last thing to think is bad. It is typically the other parts/items in the circuits that are exposed to real world exposed problems like temp and moisture and salt and such and in this case, that pcm is exposed. I really would be the last person to point at a pcm, but maybe, like the lady says, that damn thing is jinxed.

I had a pcm go bad once in my old express van. Took forever to find that was the problem. Had to replace it. Never had another issue afterwards.

 

[wifes_truck]

Hi tony, ron,

Yes I am thinking that is the only thing left, the PCM. Maybe the problem is actually inside the box itself and this is the unseen ghost. as said all the wires going into it are spotless. That's where the head scratch comes from. Now question remains... bother with second hand and getting another problem child (possible) or biting the bullet and saying ouch to chevy on a 16 year old truck ...LOL should try a scrap yard 1 first to see if that changes anything i guess.

thanks guys, cheers

 

[mikeyss]

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?

 

[wifes_truck]

hi mike.

I don't know how the fan(s) could be shorting, but you make an interesting question as only the drivers side fan is the one that I have been un-hooking and not the passenger side. The test light turns on instead of the fan being plugged in, so maybe i should leave driver side plugged in and test the passenger side. never thought about the other fan, but they are wired together in same configuration.

thanks

(PS) but that still doesn't answer the why the fans kick in 4 hours after the ignition is killed and no key in the truck.

 

[Tonyrodz]

Hi tony, ron,

Yes I am thinking that is the only thing left, the PCM. Maybe the problem is actually inside the box itself and this is the unseen ghost. as said all the wires going into it are spotless. That's where the head scratch comes from. Now question remains... bother with second hand and getting another problem child (possible) or biting the bullet and saying ouch to chevy on a 16 year old truck ...LOL should try a scrap yard 1 first to see if that changes anything i guess.

thanks guys, cheers

You won't be able to plug in a used pcm--it won't start. You can buy a good used pcm and have it flashed/programmed for your vehicle. I bought a brand new pcm for $200, and paid around $150 to get it flashed. These prices were in my area, yours may differ.
EDIT--Try looking into this--https://www.amazon.com/dp/B07N98MBR9/ref=cm_sw_r_cp_apa_i_I6H8Fb7A46ESF

 

[wifes_truck]

Hey All,

Can anyone supply me with a real PCM wire plug code for a 2005 Tahoe? I am on this circle jerk merry-go round in google hell trying to find a wire diagram for this PCM. I want to double check the wires and the situation to the pins. Nothing I am finding is coherent to what I am seeing in the physical plugs versus the wire diagrams on line. From any wire diagram I am seeing that shows the relays and the PCM say/show:

High speed / low speed

Bank c1 = 80 BU
Bank c2 = 80 GN

Problem is, all diagrams I am finding show no such wires at those pin numbers. cannot find the proper PCM schematics

Nothing in this basic diagram states what actually sends the signal to the (PCM) to engage the fans. what/where is the sending unit that turns on the relays? or grounds the relays? or how does the signal get to turn on the fans at 200 degrees or what have you...

I will be putting the truck back into the shop soon to physically pull out the PCM, open wide the pin connectors, and I mean go over every wire that is in that group/plug to eliminate any signs or corrosion. is there a way to OPEN a PCM and inspect for corrosion? or it a sealed unit with no access?

cheers and thanks.

(still haven't ruled out plan B and re-wiring in a after market fan controller.)

 

[Tonyrodz]

Hey All,

Can anyone supply me with a real PCM wire plug code for a 2005 Tahoe? I am on this circle jerk merry-go round in google hell trying to find a wire diagram for this PCM. I want to double check the wires and the situation to the pins. Nothing I am finding is coherent to what I am seeing in the physical plugs versus the wire diagrams on line. From any wire diagram I am seeing that shows the relays and the PCM say/show:

High speed / low speed

Bank c1 = 80 BU
Bank c2 = 80 GN

Problem is, all diagrams I am finding show no such wires at those pin numbers. cannot find the proper PCM schematics

Nothing in this basic diagram states what actually sends the signal to the (PCM) to engage the fans. what/where is the sending unit that turns on the relays? or grounds the relays? or how does the signal get to turn on the fans at 200 degrees or what have you...

I will be putting the truck back into the shop soon to physically pull out the PCM, open wide the pin connectors, and I mean go over every wire that is in that group/plug to eliminate any signs or corrosion. is there a way to OPEN a PCM and inspect for corrosion? or it a sealed unit with no access?

cheers and thanks.

(still haven't ruled out plan B and re-wiring in a after market fan controller.)

As far as I know it's a sealed unit--I could be wrong tho.