Po641 when it rains

[Kbake]

When it rains I get po641 code. Truck goes to reduced power. Only when it rains. Last week the truck set for 4 days while in florida the code was there when the truck was first started. I unhooked both batteries turned the head lights on for 20 min. After that the truck was fine for 2 days of driving in dry conditions. Yesterday drove into some rain it started to throw the code at 70mph pulling 20ft trailer. I could reset it quickly with my code reader. It would be ok for 5 miles and do it again about 20 times. Finally drove out of the rain and it rain perfectly for 800 miles. This has happened in the past a few times. Again only in the rain. I plow snow with it. Never had the problem. I have checked wires recovered them. Any ideas other then a deep reservoir. Next on my list

[Ian Mills]

That code is interesting because it's just check circuit for the PCM. I would check:

1) The plug for the PCM is properly connected and not leaking water into the connector

2) The ground for that section of the harness is secure and not rusty

3) There's not a place where the wire loom is worn off or burned off where water could come in and short the wires.

 

Other than that it could be a faulty wiring harness or PCM but the fact that it's weather sensitive leads me to wonder if it's a poor connection exacerbated by water