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Discussion Starter · #1 ·
I'm having an odd issue after having a bad thermostat for 10k miles. When I go to complete the emissions cycle with a good thermostat I get super weird codes that I don't get with the emissions testing incomplete.

The car only has 40k miles on it atm. Everything but the battery is OEM mopar.

If you are familiar with the emissions cycle for the car - for one of the tests it needs ~5 runs between 30 and 40 mph with a stop and idle session for 30 seconds between each run. When I do this - on the 4th or 5th attempt I get P0038, P0030, P0522. (bad oil press switch and bad 02 sensor circuit.) I've driven the car for two years a few blocks and back home without ever letting it try this and it has never once thrown these codes in 10k miles of driving. We only took the car on trips in the winter time and the low temps kept the emissions testing cycles from even starting.

So yes, the car has a decent amount of miles on with a very low coolant temp, which I know is not good.

Then the car starts to misfire out of nowhere when the emissions system throws its codes.

Then I get P0201, 202, 203, and 204. - circuit fault out of all four injectors.

It's insane. I've taken the car on hundred mile drives with the emissions testing just flat out in not ready mode and never had a single misfire. When I shut off and restart after all of the injectors throw codes - the car runs perfectly. Really thinking its an electrical prob.

When I datalog the car and its not in emissions testing - the coolant temp hits 195, then drops to 191ish after the thermostat opens and just goes back and forth slowly. The oil pressure switch stays in "high value".

I need to datalog while doing the emissions testing, obviously. Just checking if anyone has seen this type of behavior before. I saw no precedence when I did a search.
 

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Discussion Starter · #3 ·
I mean I hear you. I will end up doing that if I don't get anywhere.

Typically when I start throwing parts at something with multiple failures over a seemingly instance-based issue I don't get anywhere. I'll data log the o2 sensors, but if they aren't dropping off voltage for afr or throwing weird values for the heaters I'm not going to pop them out until I get more data. If it was ONLY an o2 sensor issue, I'd be all for it. The oil pressure sensor and the fuel injectors suddenly going nuts with shorts don't quite lead me to think its just down to a bad o2 sensor when these circuits work fine otherwise. Could still be pcm or just a system that hasn't probed certain circuits in so long they need time to get power flowing correctly.

The car was telling me to replace the coolant temp sensor when it was just the thermostat. I could have maybe fouled the o2 sensors running in closed loop mode for so long so if I don't see any other culprit that is what I'll end up doing. I do appreciate the response.
 

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Discussion Starter · #4 ·
I'd replace the o2 sensor(s).
Hey... so... I should probably replace my oxygen sensor(s). I'm going to start with the upstream, just looking for a mopar oem sensor now.

I read the FSM section on emissions and evap and is confirmed if the oxygen sensor DTC is present as well as the o2 heater DTC - the heater must be fixed first. This is prob a bad oxygen sensor as you suggested. It's likely screwing with the fuel injectors. The oil pressure sensor is probably from when the car dies with the throttle open as I attempt to move the car with the injectors and rpm dying. I mean I hope that's all the injectors and oil pressure sensor codes are coming from. When I data-logged the oil pressure sensor for a while when the car was running correctly it showed a good value the whole time.

It just seemed so bizarre to me that the PCM could induce P0201, 2, 3, and 4 just from the o2 sensor being worse for wear. If you look at what the PCM can actually see, it could possibly make sense.

These are all assumptions, but it all tracks. Read your FSM for the description of the operation of a section when you get diagnostic trouble codes ppls. Don't just look at wiring diagrams like I kept doing.

I'll update the thread as we keep working through this.
 

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Discussion Starter · #5 ·
Popped in a new upstream. Shocked at how easy it was to replace with a short o2 sensor socket. Had it done in under fifteen minutes from getting up on the ramps. I tried to run the 30-40mph 5 times and idle for 30 seconds in between test. So far so good.... only time will tell. Taking it on a 2.5-3 hr trip tomorrow so we'll see.
 

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Popped in a new upstream. Shocked at how easy it was to replace with a short o2 sensor socket. Had it done in under fifteen minutes from getting up on the ramps. I tried to run the 30-40mph 5 times and idle for 30 seconds in between test. So far so good.... only time will tell. Taking it on a 2.5-3 hr trip tomorrow so we'll see.
Good luck, the emissions stuff can be such a PITA sometimes. I love my ecodiesel pickup but the entire DEF system causes so many problems...

At least with my SRT4 I live in a state that doesn't require what you have to do.
 

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it could have a tune on it.. and the 2nd o2 disabled hence it will never be ready..
find a buddy with hptuners download the tune and post it ($0).. bunch of us can take a look at it...
 

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Discussion Starter · #8 ·
No tune on the car. I got it from a family friend who was the original owner along with two hardcover binders w docs from any time anyone ever touched the car.

The car made the 3 hour trip up to the cabin just fine on the new upstream o2 sensor.

On the way back I got a flashing MIL after letting the car idle for about five minutes prior to departing the cabin.

Drove on the flashing MIL for about an hour (~40 miles)

Stopped and did the key dance - no code.

Started the car - flashing MIL came back after about 30 seconds.

P0300 - generic misfire code.

The car had run perfectly the entire time. It didn't miss, stutter, or stall.

Drove the car 2 hours home with a steady mil.

Drove and ran perfectly until we put the car in reverse to park it.

Then we got sudden misfires.

P0201, 202, 203 are back along with a P0038 and a p0032, and the p0300 we had originally.

I datalogged the car and the PCM suddenly shows no info from the o2 sensors when the fuel injector codes show up.

For some reason after the computer completes certain emissions cycle testing its losing o2 sensor data. Doesn't appear to be the sensor's fault at this point. I'll keep you posted. I get the sense its just me, my OBD2 scanner, and my multimeter from here.
 

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Not sure on the exact specifics of narrow bands, but a wide band o2 gives off voltage in the presence of oxygen and none (or near) without. I'd expect a misfire to cause an o2 voltage drop.

When was your last tune up?
 

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The oil pressure switch, and O2 sensors don't share any signal grounds or return lines to the PCM.....maybe an intermittent short in the harness somewhere? Like between the 2 circuits, not necessarily to ground?

Otherwise you might be right with the PCM....maybe the internal SRAM or Flash has an issue when trying to write the emissions cycle data?

Rectangle Font Parallel Slope Number
 

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Discussion Starter · #11 ·
Tbagg1ns - great appreciate this. Yeah so FOR NOW the oil pressure code is gone. Maybe it was being thrown as the car died and the switch saw low pressure enough vs rpm.

im gonna fine-tooth-comb the harness. If the o2 sensors didn’t just start reporting 0 data to the pcm when it starts to studder I would be more inclined to think pcm… but it’s just so odd that it’s literally like at the time of the car writing the emissions test completion that this happens. I’ll go through the harness asap and post my results. Gotta check my meter vs what the pcm is seeing. I don’t have a drb but I have an icarsoft cr pro and it does ok…. But don’t 100% trust it either
 

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Discussion Starter · #13 ·
It was the PCM. Having a bad coolant temp sensor for so many miles somehow like screwed up the tables for writing the emissions results, or it shorted out the control circuit for the O2 heaters. I'll take the PCM apart later and figure it out. As soon as I put the new unit on all emissions tests registered correctly and everything started working right. It's almost NEVER the PCM. After checking continuity and voltage/resistance on like 20 wires I got fed up and decided to just try the PCM even though its almost NEVER the PCM.
 
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