nthinuf

Had a P0128 'Themostat Rationality' on my 08 auto. A few searches showed some possible causes from most likely, coolant level, to a bad thermostat, and further down the list was the temp sensor. Not a single post anywhere metioned pinion factor...

I was actually in the process of flushing all of the fluids anyway, so went ahead and replaced the thermostat while flushing the cooling system. The code came back, so replaced the temp sensor, and all is good.

doh, just saw that this was an old thread and I replied before reading it all.

jeepmojo

one at my cost being 200 .00 repair from dealer i drove away only to have the codes again.
put in a new coolant temp sensor for 35 bucks problem gone. its nothing more than a scam to make you pay for repair that isnt needed is what i can see , after 3 tt and housings something didnt add up. they cant be all bad thermostats lol but thats a dealership for u
must have been a bad bunch of temp coolant sensors id imagine with all the threads ive seen on it. Amazing they dont know this by now ( old thread or not , it may help others that dont know whats going on with po128 codes) good to toss it out there to help someone and save them a hassle and $
who wants to pay someone 200 .00 and not fix the issue .

Iggieo

I removed air dam recently, will put back on and if it doesn't do the trick I will replace temp sensor.

resharp001

That air dam has zero effect on the coolant temp in the block. Honestly, if you haven't changed the thermostat lately, I'd change both the thermostat housing and the sensor. Can order both factory parts on ebay for prob $40 total.

ZebraJacket99

Just as an update to my own experience. The code ended up coming back so I changed out the temp sensor and it has stayed off now for several months. The sensor was a bit of a pain to get to as a write up said to simply remove the fender liner but after wasting time screwing with that I opted to just remove the entire fender so I could get a good angle to work.

resharp001

I did this just the other month. I'd agree that if you have the factory inner liner still, it's tricky and frustrating to deal with. I have the Ace liners. 5 mins and 4 bolts to take the liner off, and about another 5 mins to change the sensor which is then prominently there.

ZebraJacket99

Yep, It almost seemed like I could bend it back out of the way enough to reach the sensor so I tried wedging a block of wood between to keep the fender out of the way but after a few times of that failing I said screw it and pulled the whole fender.

MikeyFTL

My 2012 JK Sport had this issue (code P0128) the other day after I turned on the heater for the second time in 5 years. I live in Florida. After reading a few posts on the issue I figured the thermostat might be stuck. I turned the heater on and off about a dozen times on the way home from work one night thinking it might unstick. Sure enough, the next day my engine light went off. I didn't even need to reset the code.

swizzle

Sorry all, I know this is a really old thread, but it did help me a bit. I decided to start with the Coolant Temp sensor on the back of the engine a few weeks ago. I went in through the inner fender liner, I just used a strap to tie it back out of the way. Code came back so I went with the Air Temp sensor on the intake. Code came back. So just this weekend I replaced the Thermostat and "burped" the system (which I'll admit I had never heard of before). So far so good, keeping my fingers crossed.

ZebraJacket99

I should have followed up and updated my own experience. After coolant temp sensor swap the error was gone for a couple months but did end up returning and I had to do the thermostat replacement to ultimately solve the issue. Probably should have just started with that but oh well.