Engine Cooling fan comes on all by itself
Fan comes ON and stays On till it drains the battery.
There are few possibilities that can cause this problem:
The cooling fan can only come on with the engine off because of a few reasons.
1) The very first possibility it could be an internal problem in the TIPM.
What is TIPM?
The TIPM is the module/fuse box under the hood that controls many electrical features, one being the cooling fan. If for some reason it was applying ground to one of the relay control circuits with the engine off then the fan would run.
2) Another possibility can be wiring problem. If one of the relay driver wires between the TIPM and relays shorts to ground it will turn one of the relays on and run the fan.
3) And very much possible it can be one of the fan relays. There is a high and low speed fan relay mounted directly to the back of the fan shroud. If one of these stuck on then it would cause the fans to run with the engine off.
To start troubleshooting this problem i suggest to start by inspecting the wiring.
If wiring checks ok. No loose connection or no short anywhere,then try replacing the relays and see if that takes care of it. They're inexpensive and have a fair chance of repairing the problem.At our garage we have seen mostly the issue is weak relay,which needs replacing and such problem goes away.
Otherwise the problem would have to be diagnosed through electrical testing at the time it's acting up.
Hope this helps.
Thanks.
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