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Discussion Starter · #1 ·
Hey Everyone,


I have a 2013 Jeep Wrangler Unlimited Rubicon (just passed 60k miles) with a recurring error code P0128 that's driving me nuts. I have an Innova 3020d code reader.



This all started about 2 weeks ago. Right before my emissions test is due of course. I had an engine light error to replace the oil pressure sensor switch, which I have done and that code is clear.



After that I get the error P0128, which is one off three things it says....


1. Low engine coolant level - no
2. Leaky or stuck open thermostat - maybe? but no signs of leak or over heatingg

3. Faulty cooling fan - doubtful
4. Faulty ECT - replaced last week
5. Faulty intake air temp sensor IAT - maybe?


I am running great. My dashboard temp gauge is functioning normal, no hot readings after driving to Heber (140 miles) and back this weekend or any other time.



Does anyone have any suggestions as to what the issue is? I can't get my emissions test til I fix it and I am running out of time. If I clear it then I have to go through the drive cycle before I can get it tested and every time it does that the code is back.


Thank you in advance for any help.







Low engine coolant level Leaking or stuck open thermostat (likely) Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor

Read more at: https://www.obd-codes.com/p0128
Copyright OBD-Codes.com

Low engine coolant level Leaking or stuck open thermostat (likely) Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor

Read more at: https://www.obd-codes.com/p0128
Copyright OBD-Codes.com
 

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could be the coolant temp sensor
 

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Unfortunately, you won't get too far without a good scanner to read the engine data in real time.
Looking at the data that the PCM sees will help identify which component is setting off the CEL.
Look at the IAT and ECT before and after you start the car. No readings for either is a dead giveaway.
Then watch both values as they rise. If the coolant temp doesn't come up quickly, but does move, your thermostat is stuck open. If your fan is always on or doesn't come on byu 240*, move on to that system and repair as needed.
Watch the IAT and manually try to heat it up with a hair dryer. Don't use a heat gun or a direct flame, as they are made of plastic and it needs air moving past the heated element to read the temp.
 

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I had the same issue. Replaced coolant sensor. All good. Now if I can just figure out where my coolant keeps disappearing to. Have to add a bit every few months.
 

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make sure you get a new thermostat and thermostat housing!
 
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Discussion Starter · #8 ·
Hey Everyone,


So I replaced the intake sensor and still had the code. Then my battery died which was under warranty so replaced it and the computer/ drive cycle reset. NO P0128! However got a code P0380 which is common reading through the threads for driving with your foot on the clutch. Been driving a 5 speed for over a decade and I guess unconsciously I sometimes rest my foot there. So I drove around a bit and the engine light went away...BOOM! Double checked with my Innova code reader and all green so I went and got my emissions test which what was started this whole thing. Passed! Boom!



Then a few days later my engine light pops back on P0128. Its is haunting me now. The only two things I have not done is replace the thermostat and fan. I really feel like neither is the issue since the Jeep is not overheating and the temp gauge reads normal. Its 110 here in AZ now so I would think if I was going to overheat I would have by now. Is there a way I can check the thermostat without taking it all apart?
 

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I'd replace the thermostat. I have same issue. My temp gauge is normal, no overheating. I use my flashpaq to see my temp and the temp is not going past 175. So the computer keeps tripping the light because its not coming up to operating temp w/in the specified time.










Hey Everyone,


So I replaced the intake sensor and still had the code. Then my battery died which was under warranty so replaced it and the computer/ drive cycle reset. NO P0128! However got a code P0380 which is common reading through the threads for driving with your foot on the clutch. Been driving a 5 speed for over a decade and I guess unconsciously I sometimes rest my foot there. So I drove around a bit and the engine light went away...BOOM! Double checked with my Innova code reader and all green so I went and got my emissions test which what was started this whole thing. Passed! Boom!



Then a few days later my engine light pops back on P0128. Its is haunting me now. The only two things I have not done is replace the thermostat and fan. I really feel like neither is the issue since the Jeep is not overheating and the temp gauge reads normal. Its 110 here in AZ now so I would think if I was going to overheat I would have by now. Is there a way I can check the thermostat without taking it all apart?
 

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p0128 code won't clear ...

I need to get my inspection done but my CEL was on with p0128 code. I replaced the thermostat, drove a couple days and the CEL went off. Continued to drive for a few more days.

I still cannot get inspected (NY) because the vehicle is showing a P0128 as a "stored" code (using Foxwell NT201 OBD reader), even though the CEL is off.

Any clues on how long it takes to clear a stored code? Do I reset and keep driving until all monitors are cleared?
 

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That code means that the engine has not reached the set temp it is looking for within a specified time. I had the same thing a while back. Change the thermostat and it will go away. Cheap easy fix.
 

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Hey Everyone,


I have a 2013 Jeep Wrangler Unlimited Rubicon (just passed 60k miles) with a recurring error code P0128 that's driving me nuts. I have an Innova 3020d code reader.



This all started about 2 weeks ago. Right before my emissions test is due of course. I had an engine light error to replace the oil pressure sensor switch, which I have done and that code is clear.



After that I get the error P0128, which is one off three things it says....


1. Low engine coolant level - no
2. Leaky or stuck open thermostat - maybe? but no signs of leak or over heatingg

3. Faulty cooling fan - doubtful
4. Faulty ECT - replaced last week
5. Faulty intake air temp sensor IAT - maybe?


I am running great. My dashboard temp gauge is functioning normal, no hot readings after driving to Heber (140 miles) and back this weekend or any other time.



Does anyone have any suggestions as to what the issue is? I can't get my emissions test til I fix it and I am running out of time. If I clear it then I have to go through the drive cycle before I can get it tested and every time it does that the code is back.


Thank you in advance for any help.







Low engine coolant level Leaking or stuck open thermostat (likely) Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor

Read more at: P0128 Coolant Temperature Below Thermostat Regulating Temperature
Copyright OBD-Codes.com

Low engine coolant level Leaking or stuck open thermostat (likely) Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor

Read more at: P0128 Coolant Temperature Below Thermostat Regulating Temperature
Copyright OBD-Codes.com
As stated, I would recommend replacing the thermostat (cheap & easy). The bigger issue is the fleecing we get! The question is ”why is a slow responding thermostat tied to the check engine light ?” We already have a gauge that monitors the thermostat. This engineering only benefits the dealer. This isn’t a safety or environmental issue yet because it sets the “check engine” light on you can’t get inspect w/o fixing it. Anyone who says differently is blowing smoke.
 

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I have a 2012 jeep wrangler and i have replaced thermostat couple times with new housing and the coolant temp sensor as well. checked wiring harness and no broken wires or bent ears. so what else i have l left to check before i say might need a engine.
 
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