I'm trying to help a friend fix a P0652 (5V signal low) issue that the local Jeep dealership has tried and failed to fix twice.

The last item to test on the 5V circuit is the EGR valve. He managed to get his lil' monkey paws down there from the top and disconnect the EGR electrical terminal. This has returned the Yellow/Pink 5V circuit to 5V and fixed the limp mode issue. I'm encouraging him to run this way for a few days in order to determine that it is, in fact, the EGR valve electronics that are screwed up.

I don't mean general EGR concepts, like whether it increases or decreases combustion temperatures. I'm asking if there's anything particular to the 3.8L. For example, does this ECU retard ignition excessively if there's a P0404 EGR error? Will this ECU put the engine into limp mode after some number of miles with a P0404? Anything like that?

 

I don't know for absolutely certain, but I'm pretty sure that the PCM will use the spark tables as though there is no EGR valve opening. Basically, no harm to the engine, and that's the reason I'm fairly certain that's the failure mode for P0404 (EGR sensor rationality failure). No reason for limp mode to activate, just leave the EGR closed and run the spark timing accordingly.

Stay in touch, would like to hear how it all works out.

 

Unfortunately, my friend ran right out and bought a replacement EGR and started installing it. I stopped by to help (yeesh, that upper bolt!), and it's running properly again.

Regardless, it's good to have it documented here that, as far as anyone knows, there's nothing specific to the 3.8 that would make running with an unplugged EGR an especially bad thing.

I'll post a thread documenting what I learned from this absurdly frustrating issue.

 

Yep, that EGR is in a tough location. Replaced mine while installing a new clutch just because of how easy it was to access from the back with the trans out.