Need advice '02 Sebring 2.7L I/M readiness "goes away" and "comes back".
 

I posted last week on my DTC codes. Thanks to the advice I received on this forum, I was able to sort out the P0340 & P1391 codes by fitting a new CKP sensor and cleaning a lot of connectors. It solved my intermittent stalling problem into the bargain. But I'm still left with one problem that has me wondering which way to go.

After repairs and clearing the DTCs, I drove for several hours to get my I/M monitors ready for smog check. Many of them were showing "Ready" when I returned from my drive. When I drove again an hour later many of the I/M monitors were showing "N/A" rather than "Ready". This morning the codes are showing "Ready" again, without having done any driving or even started the engine.

Additional observations:

When chasing DTCs, I did observe DTC codes "go away" (reporting no codes) and then come back without even driving.

Smog check history on this vehicle shows smog checks were aborted for "not ready" in 2016, 2020 and 2022.

It seems that this erratic behavior has been going on for a while. Since the codes come back, I don't suspect loss of battery power to the PCM causing the loss. I'm thinking of inspecting the PCM to Data Link Connector wiring first, and if that doesn't work buying a replacement PCM.

Has anyone seen this problem before? Are there any other things I should be looking at?

Thanks!

What is the age/condition of the battery? Are the battery cables clean and tight at the battery? Chrysler computer modules do not tolerate low voltages.

I suggest having the battery load tested and the charging system, i.e. alternator, tested. I have seen a similar situation on an '06 Charger where a failing alternator was allowing an ac (alternating current) ripple that would reset the I/M monitors to a 'not ready' state (among other interesting phenomena). I am not able to say if an '02 sebring and '06 charger behave the same electrically when seeing an ac ripple though. Note though the alternantor passed when tested.

If replacing the alternator, I suggest getting a new rather that rebuild if you can swing the extra dollars. I have had more than 1 rebuild need replacing in about a year's time.

Thanks for the suggestion. I spent some time today checking out the battery and charging system. I get about 40 mV of alternator ripple on the 12V. One online reference suggested the spec limit is 50 mV, so I think I'm OK there. The ripple pattern looks uniform on the oscilloscope - not missing pulses as it would do with a bad diode. I also tried swapping in a new battery and saw the same level of ripple. Not an expert, but the charging system is looking good to me.

I was getting inconsistent scans even without the engine running, so I didn't expect that to cure my scan problem. But there could be more than one problem, so it was well worth the effort checking that out. Thanks for that thought.

40 mV is good. Did you happen to check under load? For example, headlights on, defroster on, hvac blower hi? I would expect the ripple to be consistent but sometimes changes under load.

That's a good thought. I'll look into it when I get a chance. It's easy enough to test.

My concerns were mostly motivated by the need to pass smog check. I don't know whether I accidently fixed it or just had a lucky streak, but the PCU held in there long enough for all my readiness monitors to set. I rushed to the smog check station and passed. That eased my anxiety enormously. I'll still try to get things ship shape, but for now I'm going to watch and wait. Sometimes the clues fall into place in the fullness of time.

Thanks for the great suggestions. I do appreciate your willingness to help.

Glad you passed. Been there, driving to the smog station and hoping the lamp stays off.