Anyone seen P1128 Check Engine Light?

XxsullyxX123

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Hey all,
I’m getting an intermittent P1128 over the past week (closed loop fueling not achieved bank 1). Normally this code comes paired with an o2 sensor fail code or something that causes it to go off, but it’s solo. It also isn’t all the time. It’ll clear after a few ignition cycles when it doesn’t meet the conditions. Then pop back up. It also doesn’t pop up while driving, but within 30 seconds of start up. Must be when the closed loop fueling runs its test to come off the open loop for better emissions. I’m under warranty and will end up taking it to the dealer, but just looking to see if anyone has experienced this. 2020 JLUR 2.0 engine with 20k miles. No engine issues prior. Jeep drives great, so i doubt fuel filter or any of the actual “issues” that this code gets thrown for. Seems sensor related. I have the freeze frame from the JScan app from when the active light was triggered. Just unsure of which spec is out of compliance. Searching around here and google it doesn’t seem common. Or at least not written about on here.
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mwilk012

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Ambient air temperature 140 degrees
Coolant temperature 160 degrees

Neither of these seem good.
 
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XxsullyxX123

XxsullyxX123

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The ambient air temp was def an anomaly. But perhaps the reason for the code? It was probably 80 outside. Coolant temp was low given Jeep wasn’t warmed up.
 

mwilk012

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The ambient air temp was def an anomaly. But perhaps the reason for the code? It was probably 80 outside. Coolant temp was low given Jeep wasn’t warmed up.
It could be the problem. Check again when everything has been sitting for a long time, see if it reads funny or if that data line is just garbage.

How hot does the engine get when you have been driving for 30+ minutes?

Is your engine full of coolant?

I’ll just say now I think you probably need a thermostat.
 
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XxsullyxX123

XxsullyxX123

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It could be the problem. Check again when everything has been sitting for a long time, see if it reads funny or if that data line is just garbage.

How hot does the engine get when you have been driving for 30+ minutes?

Is your engine full of coolant?

I’ll just say now I think you probably need a thermostat.
I’ve topped off the coolant (prior) and also tightened the inlet that is a common fail area. Coolant is fine. Engine runs normal range on heat seeing 190-210 normal and 220 if I’m on the gas for a bit on a highway incline. Never overheated.
 


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XxsullyxX123

XxsullyxX123

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I went ahead yesterday and reset the light and will monitor for its return. it was coming and going on it's own, but i dont know clearing it will change whatever threshold it needs to present to pop up again or not. plus i want a new "freeze frame" for if it pops up again for me to compare to. so far after 2-3 cold starts and multiple warm it hasnt come back, but im sure it will
 
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XxsullyxX123

XxsullyxX123

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So it's been a solid week and I have done a lot of driving and cold starts and warm ups etc and logged probably 300 miles since the CEL reset. It has not returned and there are no pending codes either. At this point I am assuming it must've been a fluke and a bad reading from a sensor that triggered it, but will obviously monitor.
 
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XxsullyxX123

XxsullyxX123

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Just updating this (more for future users properly using the "search" function) that the CEL continues to remain OFF after a few more weeks and around 1,000 miles in total. the computer has run through all checks and passed EVAP checks (which take the most miles to show readiness again) as well.
 
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XxsullyxX123

XxsullyxX123

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@mwilk012 the CEL came back this morning after clearing the code 1500 miles and over 100 warm ups ago. super weird! the freeze frame looks fairly similar, with modest negative LT fuel trims (vacuum leak?) IAT and AAT are both read high on the freeze frame (111 degrees each, and coolant temp 129) for 13 seconds after a cold start in a 70 degree garage.

i did cycle the jeep on and off a few times last night for under 20 seconds each time while cold to check for an exhaust leak on a newly installed muffler delete pipe. The code illuminated this morning at start up. coincidence perhaps, and maybe not related to the pipe, but related to cycling the jeep on and off quickly before it entered closed loop twice could trigger it. the CEL already shut itself back off after a few cycles.

around 1000 miles before the first CEL i put an intake in, and 500 miles before the first CEL i did an oil change. can't say its related, but just figured worth mentioning as coincidences are never my assumption for things.

Also, running live data a little while ago at ;lunchtime, all of the temps were much more normal, with AAT at ambient around 65 degrees and IAT lower as well as coolant up at 185 at warmed up idle. It did record a couple of misfires in the first few seconds of the cold start while running live data at lunchtime in cyl 1 and 2, but no codes and no more misfires after.

Despite all my googling, I cant seem to find the conditions that need to be met for the engine to enter closed loop. i wish I could find that spec, this way I could see what number is the one that is out of whack. It will be a dealer visit perhaps, as it is under warranty. I just like to troubleshoot myself.
 
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XxsullyxX123

XxsullyxX123

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Here is the freeze frame.
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XxsullyxX123

XxsullyxX123

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My guess is a bad temp sensor reading. Do you have a freeze frame from when it’s not throwing a code? If so compare the two, see what’s off.
I dont have a freeze frame, but looking at the live data, when its not throwing the code (or even after the code was thrown and still there for that matter) the IAT and AAT temps are all normal. may just be wonky readings at startup that then normalize. your guess is the same as mine. but 1500 miles and no CEL is weird. So maybe its not a bad sensor, but a sensor that every now and then gets a bad reading and i believe 2 times in a row is what throws the code.
 

58Willys

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I dont have a freeze frame, but looking at the live data, when its not throwing the code (or even after the code was thrown and still there for that matter) the IAT and AAT temps are all normal. may just be wonky readings at startup that then normalize. your guess is the same as mine. but 1500 miles and no CEL is weird. So maybe its not a bad sensor, but a sensor that every now and then gets a bad reading and i believe 2 times in a row is what throws the code.
I agree something is not reading correctly. Could be a bad sensor, bad sensor circuit, electrical interference, bad processor, etc…

I think one thing required for the system to go into closed loop, is a minimum engine temperature. A bad sensor reading that thinks the engine operating temp is low, could prevent this.

If your still under warranty, a dealer visit would be good. At least the issue will be be documented.
 
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XxsullyxX123

XxsullyxX123

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I agree something is not reading correctly. Could be a bad sensor, bad sensor circuit, electrical interference, bad processor, etc…

I think one thing required for the system to go into closed loop, is a minimum engine temperature. A bad sensor reading that thinks the engine operating temp is low, could prevent this.

If your still under warranty, a dealer visit would be good. At least the issue will be be documented.
Drove home (no CEL) with live monitoring on my JScan and Ambient temp was right on a mid 50's (the actual temp) and the IAT was within +5 to +15 degrees of the ambient the whole ride. Weird that both the Ambient and IAT sensor would BOTH show ridiculously false high temps at the same time on a cold start and both be bad, and then both be working. Also curious if there is a potential PCM feature that doesnt allow a reading on the IAT to be significantly below Ambient, and accepts the ambient value as an IAT in that event. Meaning Ambient sensor showed 111 degrees on a cold start in a 70 degree garage, so IAT was forced to accept that value. In no way was that anywhere near the actual temp at the time the code was thrown. Either that, or as you said the circuit (maybe fuse?) or PCM itself. I'll get to the bottom of it one way or another lol

 

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