can someone please explain some of the major differences in these pcms? Thank you.

 

obd2 is much more complex, has a lot more dtcs and diagnostics.

 

The basic logic for fuel and ignition control is similar when comparing the LT1 OBD-I to OBD-II PCM's. The main difference is the fact that they added a few sensors (crank position, after-cat O2's, EVAP vacuum switch) and a lot more diagnostic checks, all of which are aimed almost exclusively at emissions. The diagnostics typically have little, if anything to do with fuel and ignition control. There was some modification of the A4 control logic, which appears to overcome problems with high stall converters that were in the OBD-I system.

 

Also, sadly, the performance shift mode switch feature doesn't work on OBD2 PCMs...