[JessGerr]

Hi all!
I’m new to this forum but have an issue with my 2019 Jeep Cherokee Trailhawk that NO ONE can figure out. It has been to 3 different Jeep dealerships and multiple “ma and pa” mechanic shops and no one has been able to solve this.
So what I’ve noticed is ONLY in the winter my car has random misfires while idling only. Once I start driving it stops and will come back when I’m either parked or at a stoplight. The check engine light will either pop up with a message to “service stop start system” accompanied by the A with and arrow and exclamation point or just the check engine light will start flashing. The codes that are populating are P0300, or P1129. First time I had this issue was a little over a year ago (2021) around December and it only happened once last year and now this year it’s happened more times that I can count. The dealerships say bring it in but then they turn the car off and everything stops and when they turn it on they can’t make the misfire happen again so they say to come pick it up. From all the times it has been happening they have recommended I get an oil change, switch gas, get a new battery, flash my O2 sensors, reset the PCM, flash the system for any updates, and change my spark plugs and coil packs or have just said they have no clue and sent me on my way. I have done all of the maintenance listed above but my car still continues to misfire and none of my mechanic friends, or the shops can figure this out.
I was just curious if anyone on here has any more ideas on what it could be.
I have attached photos of what happens during the misfire and what pops up on my screen. I don’t know why but it’s not allowing me to upload the videos of it. Thank you for any responses and ideas!

 

[Mark_]

HI and welcome

Yeah, forum won't let us upload big files. Best way is to host on YouTube, then post the link here (YouTube or similar).

That is a weird problem. Seems dealer has covered the basics and threw the usual parts at it.

Before we dig any deeper : which engine ? Mileage ?

P1129 is not a common code on these Cherokees. From what I read online, there could be other sensors involved (other than the O2 sensor).

 

[Steveinmedford]

1st. Check your battery. Has it been replaced since 2019? Surprising what a weak battery issue can affect.
2nd Maybe an O2 cell gone bad?
3rd The misfire code is a common CEL code. Search for misfire and you'll find a bunch listed.
My 2014 had the P0301 code, cyl 1 misfire. Engine ran rough until warm up and smoothed out after. This condition has come and gone for awhile. Especially during cold weather although I havent seen for awhile, considering it was -10° last week.
The P1129 I'm not sure about. P1129 Jeep Code - Closed Loop Fueling Not Achieved Bank 2.

Read more: https://www.autocodes.com/p1129_jeep.html

Maybe try a few rounds of fuel injector/engine cleaner. I've used.....
Liqui Moly 2037 Pro-Line Engine Flush

Please let us know any follow-up/issue resolve.

Good Luck

 

[JessGerr]

Hi all!
I’m new to this forum but have an issue with my 2019 Jeep Cherokee Trailhawk that NO ONE can figure out. It has been to 3 different Jeep dealerships and multiple “ma and pa” mechanic shops and no one has been able to solve this.
So what I’ve noticed is ONLY in the winter my car has random misfires while idling only. Once I start driving it stops and will come back when I’m either parked or at a stoplight. The check engine light will either pop up with a message to “service stop start system” accompanied by the A with and arrow and exclamation point or just the check engine light will start flashing. The codes that are populating are P0300, or P1129. First time I had this issue was a little over a year ago (2021) around December and it only happened once last year and now this year it’s happened more times that I can count. The dealerships say bring it in but then they turn the car off and everything stops and when they turn it on they can’t make the misfire happen again so they say to come pick it up. From all the times it has been happening they have recommended I get an oil change, switch gas, get a new battery, reset the PCM, flash the system for any updates, and change my spark plugs and coil packs or have just said they have no clue and sent me on my way. I have done all of the maintenance listed above but my car still continues to misfire and none of my mechanic friends, or the shops can figure this out.
I was just curious if anyone on here has any more ideas on what it could be.
I have attached photos of what happens during the misfire and what pops up on my screen. I don’t know why but it’s not allowing me to upload the videos of it. Thank you for any responses and ideas! View attachment 222400
View attachment 222401
View attachment 222402
View attachment 222399

HI and welcome

Yeah, forum won't let us upload big files. Best way is to host on YouTube, then post the link here (YouTube or similar).

That is a weird problem. Seems dealer has covered the basics and threw the usual parts at it.

Before we dig any deeper : which engine ? Mileage ?

P1129 is not a common code on these Cherokees. From what I read online, there could be other sensors involved (other than the O2 sensor).

It has the 3.2 V6 and just under 62,000 miles on it right now.

 

[JessGerr]

1st. Check your battery. Has it been replaced since 2019? Surprising what a weak battery issue can affect.
2nd Maybe an O2 cell gone bad?
3rd The misfire code is a common CEL code. Search for misfire and you'll find a bunch listed.
My 2014 had the P0301 code, cyl 1 misfire. Engine ran rough until warm up and smoothed out after. This condition has come and gone for awhile. Especially during cold weather although I havent seen for awhile, considering it was -10° last week.
The P1129 I'm not sure about. P1129 Jeep Code - Closed Loop Fueling Not Achieved Bank 2.

Read more: https://www.autocodes.com/p1129_jeep.html

Maybe try a few rounds of fuel injector/engine cleaner. I've used.....
Liqui Moly 2037 Pro-Line Engine Flush

Please let us know any follow-up/issue resolve.

Battery is good, I have a new one in there as of 2-3 months ago, the dealership supposedly cleared everything with my O2 sensors and said it wasn’t anything related to that. (It did throw a code for them originally like 3 months ago) But that was fixed.
And they just needed to be flashed. And it has never thrown another misfire code other than the 300 one. There had never been a destination for them to narrow the misfire down to. I will bring up possibly using the fuel injector to one of my buddies, because as of now he was saying it was best to not put any additives in it while it’s acting up. Thanks for the response!

 

[sanghill]

Seems like a sensor not measuring the ambient temperature correctly and it is running lean when cold.
Has the engine air cleaner been replaced recently? The engine may be running lean.
Are you using any aftermarket air inlet systems? A CAI can keep the incoming air too cold.
Listen for the infamous valve train tick, certainly the Jeep dealer would catch this one.

 

[Mark_]

Seems like a sensor not measuring the ambient temperature correctly and it is running lean when cold.
Has the engine air cleaner been replaced recently? The engine may be running lean.
Are you using any aftermarket air inlet systems? A CAI can keep the incoming air too cold.
Listen for the infamous valve train tick, certainly the Jeep dealer would catch this one.

From the code description :

Code P1129 Jeep Possible Causes
Fuel delivery system
Engine Coolant Temperature (ECT) sensor or wiring connectors
MAP sensor or wiring connectors
O2 sensor wiring or connectors
Engine mechanical system

Read more: https://www.autocodes.com/p1129_jeep.html