2003 Ford Excursion VIN: 1fmsu43px3eb55395
 

Excursion ran well & pulled well

~ batteries draining overnight
~ one evening tranny went into limp mode.
~ cannot read codes as snap on tools indicates "no communication"
~ after a week of sitting start would not work unless crossed at pole
~ changed out PCM (beside battery):
......... now starter works without crossing!
......... batteries still drain
......... no communication from OBD-II
......... tranny still in limp mode

No communication with snap on scanner is usually blown fuse or bad cable or connection. What scan tool are you using? Does it have " keys" ? You may have a bad key. Your snappy dealer should be able to help with cable and keys.
You can do simple test to resolve battery issue.
First make sure both batteries are good! Bad batteries can be shorted internally and will make u crazy.
Disconnect both batteries positive cables. Leave neg cables. Connect volt meter between pos. cable and battery. You will see a draw if there is a problem. Pull fuses till your draw goes away, you have found problem circuit! Now the fun begins as you narrow down further!

~ thanks
~ no blown fuses
~ have proper key for OBD-II
....Strange why no communication from OBD-II
....Strange how PCM exchange corrected starter

could starter be shorting out? and cause havoc everywhere?

Usually if you find communication problem u find problem with vehicle. At least that's my experience. There could be a ground problem too which I have seen cause weird issues with computers in vehicles. Rust and corrosion in weird places makes gremlins. And yes starter issue is weird!

we will keep looking and keep everyone posted.
~ if anyone has any more ideas please let us know ASAP