Anyone seen P1128 Check Engine Light?

[JeepersTodd]

mine would only come on every 1000 miles or so after clearing and now its been 6,000 miles and no CEL. that being said, its been colder out. so the jeep expects to be cold on a cold start whereas i was wondering if on a warm day cold start any funky temp readings throw the code. unsure.

As I believe I said before, after they fixed the o2 sensor (and said it came back on for them at the dealer) when i got it home i disconnected both PCM wiring harnesses and check to see if the pins were all seated right and blew on it and popped them back together. was that the fix or coincidence?? i have no idea. but easy and worth a try. Intermittent issues are the hardest to find, but normally mean no component is actually broken (or it would throw a different code along with the P1128) but maybe just a connection is lost for a second in the wiring. its worth a try!

Indeed true. You guys are great. I've read through this post a million times lol! I haven't had any other codes set, but I did pull the two connectors off the PCM like you talked about and everything look normal there. The locks on the connectors firmly snap into place and the pins were all straight and clean. I did the pull and wiggle test on what parts of the engine harness I could access, but I never had the MIL or any codes set while doing such.

I'm pretty sure the coolant loss issue I had is fixed now. I did notice a very faint exhaust odor near the turbo once, but I've never noticed an audible exhaust leak. Mine's all stock. I know leaks near an O2 sensor can sometimes mess with the O2 readings, but I'm not getting any O2 codes.

Will keep in touch.

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[Heimkehr]

when i got it home i disconnected both PCM wiring harnesses and check to see if the pins were all seated right and blew on it and popped them back together.

Just curious: did you disconnect a negative battery cable so as to eliminate the risk of the PCM being energized, before removing the harness connectors?

 

[XxsullyxX123]

Just curious: did you disconnect a negative battery cable so as to eliminate the risk of the PCM being energized, before removing the harness connectors?

I did not. oops lol

 

[mchrisferraro]

mine would only come on every 1000 miles or so after clearing and now its been 6,000 miles and no CEL. that being said, its been colder out. so the jeep expects to be cold on a cold start whereas i was wondering if on a warm day cold start any funky temp readings throw the code. unsure.

As I believe I said before, after they fixed the o2 sensor (and said it came back on for them at the dealer) when i got it home i disconnected both PCM wiring harnesses and check to see if the pins were all seated right and blew on it and popped them back together. was that the fix or coincidence?? i have no idea. but easy and worth a try. Intermittent issues are the hardest to find, but normally mean no component is actually broken (or it would throw a different code along with the P1128) but maybe just a connection is lost for a second in the wiring. its worth a try!

I had the same code come up over the past few weeks as it has been crazy hot here in Texas and I was wondering the same thing about any funky temp readings throwing the code, based on the the following:

My garage is east facing and heats up like crazy in the morning (separate issue, which I'm working on), but it would be close to 100 in the garage and then I'd back out and the ambient temp would drop to 75-80 instantaneously (outside temp) and then the light would come on several seconds later.

As an experiment, I've been opening the garage about 10 minutes before start up, letting the temp equilibrate and then not backing out until at least 30 seconds after starting the jeep, and no light since. It has been about 30 start ups and 1000 miles and no light. I bring this up because I would think that would be an unusual or abnormal reading where one of the temps dropped by 20-25 degrees, which I'd imagine would be different than what the Jeep expects on a warm up, and possibly throw the code.

I could be way off base, but wanted to get some thoughts about this being a possible cause.

 

[XxsullyxX123]

I had the same code come up over the past few weeks as it has been crazy hot here in Texas and I was wondering the same thing about any funky temp readings throwing the code, based on the the following:

My garage is east facing and heats up like crazy in the morning (separate issue, which I'm working on), but it would be close to 100 in the garage and then I'd back out and the ambient temp would drop to 75-80 instantaneously (outside temp) and then the light would come on several seconds later.

As an experiment, I've been opening the garage about 10 minutes before start up, letting the temp equilibrate and then not backing out until at least 30 seconds after starting the jeep, and no light since. It has been about 30 start ups and 1000 miles and no light. I bring this up because I would think that would be an unusual or abnormal reading where one of the temps dropped by 20-25 degrees, which I'd imagine would be different than what the Jeep expects on a warm up, and possibly throw the code.

I could be way off base, but wanted to get some thoughts about this being a possible cause.

I wouldn't say way offbase. that totally seems like it could be a reason. if a few of us get these codes and can't really find a solid answer why, or something broken, then these other factors seem plausible.

 

[JeepersTodd]

Mine seemed to set the code a lot more often once it first started setting. At that time it was our cold and rainy season. Seemed like as we went into dryer and warmer weather (mornings), the code set less often on mine. But then too... I had been pulling stuff apart and replacing parts. So I could not say for sure what was causing the code to set less often. It's summer here now and were having 90-100F days. With that, mines gone weeks at a time not setting the code now.

 

[XxsullyxX123]

Mine seemed to set the code a lot more often once it first started setting. At that time it was our cold and rainy season. Seemed like as we went into dryer and warmer weather (mornings), the code set less often on mine. But then too... I had been pulling stuff apart and replacing parts. So I could not say for sure what was causing the code to set less often. It's summer here now and were having 90-100F days. With that, mines gone weeks at a time not setting the code now.

did you ever try to change to upstream o2 sensor? i still dont know if that is what fixed mine or just playing with the PCM harness.

 

[JeepersTodd]

That was the last thing we tried on mine, replacing the upstream 02. It's not set the code for a while now... but it's done that in the past too. I'm still not considering mine fixed. I've seen a bunch of tech's fighting this same code on 2020 2.0L Wranglers, all throwing PCM's and 02 sensors at these and never fixing the issue. I still say this will be "fixed" by Chrysler coming out with a PCM flash to adjust the PCM programming eventually. But that's just my hunch. I'm also curious if all these Wranglers setting the P1128 are doing so for the same reason, or if there's multiple issues causing this code for different folks.

 

[XxsullyxX123]

That was the last thing we tried on mine, replacing the upstream 02. It's not set the code for a while now... but it's done that in the past too. I'm still not considering mine fixed. I've seen a bunch of tech's fighting this same code on 2020 2.0L Wranglers, all throwing PCM's and 02 sensors at these and never fixing the issue. I still say this will be "fixed" by Chrysler coming out with a PCM flash to adjust the PCM programming eventually. But that's just my hunch. I'm also curious if all these Wranglers setting the P1128 are doing so for the same reason, or if there's multiple issues causing this code for different folks.

i just rolled 35k miles on mine and havent seen the code since 23k-24k i forget exactly. So weird. always drove fine though which is good

 

[JeepersTodd]

Glad to hear it. Yeah, this code basically just sets when the PCM sees "something" not being within its parameters to allow for the switch from open to closed loop fueling after a start up, whithin the time allowed. That's it really. It could be something very simple that isn't getting to the correct point within those 13 seconds (that's what mine takes to switch from open to closed). If that's the case, the PCM sets the P1128. Pretty lame how Chrysler has the PCM programmed to set this code as a one trip fault and instantly turn on the MIL. Again, why I think they messed up and will eventually adjust something in the PCM programming to fix this with a flash update. At least make the PCM less sensitive or to set the MIL only after a two trip fault or something. Indeed, I have yet to find anyone fighting this code who has ever noted any drivability issues thankfully. Chrysler did something similar when this body style came out a few years back and the manual 3.6L Wranglers were setting misfire codes like crazy. Their fix was to basically make the PCM less aggressive with how it counted/calculated misfires.

 

[XxsullyxX123]

@Heimkehr @JeepersTodd

I'm curious if this PCM flash customer satisfaction notice Y40 a bunch of us are getting in the mail has any connection to this issue. 43k miles now and no P1128 in well over a year and ~20k miles. A fluke that the O2 sensor fixed on mine.

 

[Heimkehr]

@Heimkehr @JeepersTodd

I'm curious if this PCM flash customer satisfaction notice Y40 a bunch of us are getting in the mail has any connection to this issue. 43k miles now and no P1128 in well over a year and ~20k miles. A fluke that the O2 sensor fixed on mine.

I've received no such mailing, but then again, I've not turned over my Jeep for a PCM flash that may be or is related to the recurring P1128 CEL.

 

[XxsullyxX123]

I've received no such mailing, but then again, I've not turned over my Jeep for a PCM flash that may be or is related to the recurring P1128 CEL.

yea they never reflashed mine either. a bunch of 2020 2.0's got the letter end of last week. a few guys on here mentioned it too. it has to do with whatever the stock flashing is and some issues with CELs and emissions. thats why i was thinking maybe they finally had a fix for these random PCM codes when everything else seemed to work fine. I was just guess though.

 

[XxsullyxX123]

pic of the notice

 

[JeepersTodd]

@Heimkehr @JeepersTodd

I'm curious if this PCM flash customer satisfaction notice Y40 a bunch of us are getting in the mail has any connection to this issue. 43k miles now and no P1128 in well over a year and ~20k miles. A fluke that the O2 sensor fixed on mine.

I'm still assuming that replacing the upstream (wide band) O2 sensor was what fixed the problem child 2020 I was dealing with. No news is good news.

I just read over the Y40 recall notice that Chrysler published on their dealership page in their service library for their techs. They do list a few codes there that the PCM flash addresses, but the P1128 code is not one of those codes. They do say however that the flash also addresses certain emissions related issues that is required by the gov. So only engineering knows that for sure... and they are very, very, very tight lipped.

I said from the get-go while diagnosing my P1128 that this issue was software related and it would eventually be fixed with a flash (software update). Only time will tell but, looks like that may likely be the case. Thanks for the update here in regard to y'all getting the recall notice. Was interesting seeing on that same recall, there's four different vehicle groups this software update addresses. About half of those are hybrids too. Weird.

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