I'm going to look at a 2004 F150 this weekend and thought it might be a good idea to take my scan tool with me and hook it up when we test drive it to check out the the live mode readouts, if they let me. Does anyone know where I can find out what the numbers should read ahead of time so I can tell if there is an issue?

 

If any of the sensors are out of value you will have a CEL.

I would look for a CEL, and also the readiness indicatirs to make sure there were not any recently cleared codes that they are hiding from you.

The codes won't be there, but if all the readiness indicators are not in the proper position you'll know there was a recent repair, clearing of data, or the battery was disconnected for some reason.