2002 GMC Sierra PCM

I just had my truck detailed and they power washed my engine. Since then my battery light keeps coming on. Took it for service and they asked me if I had the engine cleaned recently. Said water probably got into the PCM and it might need to be replace and I should take it to a dealer. Very expensive. Codes P1637 & P1638 were set. Really? The brain of my truck needs to be replace due to moisture? They did all the standard tests and everything checked out ok, truck runs fine. I just read on another question that the PCM's dont go out very often? I should check for/ask dealer to check for specific shorted sensors? Please educate me.