If the unit has a split harness with 3 connectors near left tilt cylinder behind the plastic, my be you have the 2 large connectors crossed. normally when these codes are expressed, in my experience you have a ecm issue.

Partsguy5 I realize that I saw a post that pertained to the code issue I was dealing with and was trying to figure out what this person did to fix it yes the truck is a p5000

Grant,

According to the serial number your truck is either a P4000 or P5000 so you may not have the correct ECU.

Ok So the ECU issue The cat dealer tech had pulled the original ECU and put another one in. If in fact this is the correct ecu for this truck Im not sure all I know is that The tech couldn't get anything to work he plugged in his laptop and it wouldn't even pull up the truck info No Communication also upon first receiving the truck the OBD2 plug wouldn't even power up the scanner so I called into independent lift truck of Alaska and talked to service there they informed me that they have seen a lot of issues with these wiring harnesses in this series of P5000 truck Serial # is AT3512277 so I checked all relay boxes and fuse panels for power and for corrosion on the terminals they all looked fine no blown fuses. Also checked the VSM plugs and ECM plugs there wasn't any corrosion at all. That was when we replaced the wiring harness ordered from cat for the proper serial number build date ETC... I realize these computers are truck specific if you will but the basic premise is still the same. Some of the parameters might not be exactly right but should be enough to run the truck

Have you checked your fuses? A blown fuse will cause no communication.

when you say "switched out old card with new one" i assume you ordered it from cat and provided all the information on the truck when ordering? Model, serial number, old ecu number etc?
These ecu's are generally programmed by the factory based on your serial number build. If you just grabbed one out of another truck or just ordered one out of the manual and threw in on the truck that's probably not going to work.

As for the com errors you must have some plug connection issues at the ecu or somewhere on the truck. I'd check the relay box's also and make sure those connections are clean, both box's, not just the one under the hood.

btw... what is the serial number of this truck?

Yes i have verified all the wiring under the dash. This truck did have a lot of corrosion on the plugs ( Ign Switch, Trans Power-soft Switch and light switch) I have checked all the plugs the rest seem to be fine brand new wiring harness because we were told that was a known issue from several cat dealers truck has a build date of 1-21-08. Before we changed the wiring harness couldn't get an OBD2 to even turn on Cat dealer tried to hook up the lap top with the same outcome no com. That tells me we are getting there just cant figure out why I cant get communication

have you checked the wiring under the dash?

Did you ever figure this out having the same code issue on a P5000 replaced harness and still same codes