I just got P0128 code on my 2016 JKUR. I read about what that means but I have a question.

The temp on the instrument panel seems to come up as fast as usual. It settles mid-scale, which is where it always is. To me that says thermostat is ok. The heater works great. If thermostat were stuck open I would expect temp to never reach normal operating range and heater would never get warm.

I had a truck do that once before. The heater never got warm, the defroster didnt work, etc.

Does the instrument panel temp come from a different sensor?

Also, we have had a sudden cold snap. Could this be weather related? Why now?

 

This is crazy: I started getting that on my 2014. I clear the code, stays good for quite awhile, then comes back again. I'm in NJ. I reached out last week to a friend in Georgia who also has a Jeep. Coincidentally he said the same exact thing has recently happened to his 2012 Jku. I bought the t-stat with housing and a radiator funnel kit, but have not done the job yet. Although I'm getting the error code, the Jeep runs fine, temp looks good, heat works fine. There is also a temperature sensor that could be the fault, but I figured I'd do the T-stat first.

 

On these things it's often not a terrible idea to replace that sensor at the same time as the thermostat. It's not much money. I'd say it's really quick to do as well cept I don't have factory fender liners to get in the way. Without fender liners it's literally 5 min job to swap that out and you only lose about 1/2c coolant if you're quick (simple sensor inserted into the driver's side of the block that you access from the wheel well). I recall having that code one time. replaced the sensor and it was ok for a while then came back. Swapped the thermostat and never saw the code again. I will say that prior to swapping the thermostat, I noticed nothing abnormal at all.....similar to the OP.

 

I watched one YouTube video where the guy hooked a ratchet strap to the fender liner to pull it out of the way enough to create a space for his arm to fit in to reach the temperature sensor. He was able to replace the sensor without removing the liner.

 

Usually this is the thermostat but if everything else is Ok then it is probably the sensor. You can always test the thermostat once you get it out but at that point I would just put a new one in anyway.

 

Watch the temp live data and see if the temp sensor is linear and correct. This is common on these. Ive swapped many of both parts but . 90% were the thermostat. No point screwing with a good sensor. Many, if not most, had no symptoms really.