This is a 2002 grand Cherokee with a 4.7L. I bought it knowing the battery was shot, and the vehicle, even with a jump, wouldn't start. Got a new battery so I could run diagnostics on the no-start. Found a faulty cam sensor & changed that out. Now starts/runs great, but the alternator wasn't charging. So I replaced the alternator, only to have the same issue. I checked for voltage at the red lead at the alternator and got battery voltage, but still went ahead and ran continuity checks on both the power & ground circuits, and the alternator body itself is continuous to the B- post. So, I found a schematic of the charge system & checked continuity from the Wh/Rd wire to PCM C3-25 (ok) and the DG wire to PCM C2-10 - both checked good. However, I noticed that these two generator control circuits, both routing to the PCM, or, rather, did not notice, which circuit should carry what voltage or if it acted as a ground. I hooked the PCM back up, set the key to the run position (not start) and checked both wires for power and ground - nothing. I also checked for a possible short in between the two wires - nothing. I figured a failure in the generator control circuit should trigger a code - nope. I'd hate to think it's a PCM issue, as in looking at the pinouts, there are a lot of things that shouldn't be working right if there was a PCM internal failure. It doesn't seem likely to only have an internal failure of the generator control/driver circuits. So, help?

 

With no options, it seems, I have ordered a 'plug&play' ECM. It is due to arrive on or about the 10th. Will keep the group apprised. ... I know I proposed a condition that, without actually being here, may be difficult to contemplate. for that, I apologize.

 

ECM came a couple days later than expected, but got it installed. All systems now working normally. The only thing I can presume is something, at some time, occurred on that alternator circuit that created an internal short at the ECM. I thank all who read my post, and appreciate their contemplation.