I just purchased a 2005 T&C touring with the 3.8 engine. 68000 miles. It runs and drives great.

The battery light has been on. I replaced the battery and alternator but the battery light and check engine light are both still on.

I am getting the following codes.
P0645 - A/C clutch relay (the relay is good)
P0443 - Evap purge control system
P0499 - Evap system vent valve
P0622 - Generator field not switching
P0403 - EGR valve

My next step will be to check and clean all ground connections, and look for loose or frayed wiring.

Could I have a bad ECM? and if so, how do I diagnose that?

Any help would be appreciated.

 

Have you checked fuses and connections(grounds)? Not often to hear of replaced alternators not working and keeping the battery light on. Hope it was a reman alternator as the 3.8 uses a clutched pulley drive and can go bad not "hooking up" to the alternator shaft to allow it to charge. Have had that happen to me on 2 of my past vans.
As for the other codes... sounds like you have other concerns to be checking out, AFTER getting the charging system working.

BTW: Have you confirmed voltage output(charge) with a voltmeter?