I have a 2012 JKUR, built in Mar 12, I received it in Apr 12, 25,000kms. AEV 2.5 lift, 35 inch MTRs, exhaust spacers, axle gussets, trektop, otherwise bone stock. The reason I mention these small mods will be clear below. This is a stock drivetrain problem, but maybe I started the thread in the wrong location.

Started to trip the P0128 code after about 4 months. I cleared it, checked the coolant levels and everything was fine. Talked to the dealer, they confirmed the coolant temperature was too low for what the computer thought it should be hence the code. Said to bring it in when I had a chance. This is my "work" vehicle so it took a few months before I got it to the dealer. The code flashed once or twice more but I cleared it, checked fluid levels etc and moved on.

Dealer replaced the coolant temperature sensor and housing about two months ago. I understand they are one and the same? Code went again the following day.

The dealer had the jeep for 2 more days, said everything was fine and the code is tripping because of the larger tires and lift. The service manager said he conferred with Chrysler engineering and they say the pinion factor in the computer is wrong for the size of tire on the jeep. I was told my pinion factor was set for a 225 tire. Mine was a Rubi and had 255's, so I pointed out the factor was never correct and using his logic and should have tripped codes from the beginning. I did the lift and tires within the first 4000 kms, so maybe it didn't run long enough to cause trouble.

The service manager said they set the pinion factor to the largest setting and I would have to live with the code coming on every so often. I believed this to be bullshit, but thought I would try it. The speedo was now reset to stock when I got the jeep back, I have the AEV plugin and had adjusted it when I lifted the vehicle. I drove like this for a couple of weeks, then the code came back. I reset it, fixed my speedo calibration, and the code came back a week or so later.

Now it's coming on every other day or so. To me, something is changing and getting worse. I do not know if they changed the thermostat itself. I do not hear the famous 3.6 litre ticking sound, but have not performed a leak down test. No noticable lack of power.

I plan on heading into the dealer tomorrow to discuss. Nothing ever gets solved over the phone. I'm thinking the thermostat is sticking or broken, based on online searching for the problem. I don't know if it was replaced or not already. I can't find the invoice they gave me last time, but I believe only the temp sensor and housing were listed.

Does anyone here have anything else they can offer me for advice? Have I overlooked something, or are they telling me the truth?

Thanks, sorry for such a long read.

 

Sorry my first sentence is confusing. I custom ordered this vehicle, it was built in Mar 2012, received it in Apr 2012. It now has 25000+ kms.

 

That is typical bs. Check your coolant level. If not my guess is your thermostat. Is your heater working? Could also be the iat sensor throwing of the test. Did you reprogram your fan to run more or is it running a lot?

Sent from my Galaxy Note 2

 

I get lots of heat, tons. Coolant level is fine, I check evertime the code trips, just in case. I haven't changed anything with the fan or any other programming I only have the AEV module. But I couldn't tell you if it runs often or not, I can't hear it while I'm driving.

I did remove the lower air dam, or deflector below the front bumper, would this influence the cooling system? It was interfering with the tires even with the wheel spacers. I have recently purchased the steel to build new bumpers and figured I would make a removable skid plate for below the bumper.

 

Nah that wouldn't do it. You should take it to another dealer or talk to the service manager.

They always blame the tires and lift. Ask him how the larger tires are making your coolant temperate too low. That makes no sense. They replaced the sensor that compares its temperature to the iat sensor. It is the one on the flexible intake tube to your throttle body. If the intake air is hot and the other is cool it throws the error. Could be a bad iat (prob not. . Make sure it is seated properly) or intermittent ground. These things are hard to chase and cost the dealer money. Dont let them play you.

I'm no expert on this stuff. Maybe sometime else will come in. If you feel like messing with it, check this out.

http://www.youtube.com/watch?v=dM4zUa9-Ib4
Sent from my Galaxy Note 2

 

Just an update;

ServiceManager was standing behind the engineering statement of the oversized tires causing the P0128 code. He stated the vehicle had been modified by the tires, tires causing the failure, and therefore warranty is void.

I asked to see any and all documentation which might stand up in court regarding oversized tires causing the coolant temperature to be too low. Could Jeep prove to a court they do not promote or encourage the modification of their vehicles. I reminded him I would first enter the MOPAR accessories catalogue into evidence. I also reminded him of the $80K large I spent at the dealer last year between the jeep and my ram.

Long story short, they are now being very helpful. Warranty argument aside, he agreed the P0128 code now trips with increasing frequency, a clear signal of a failure worsening. I do understand without factory support to cover his costs he doesn't want to stick his neck out too far. He arranged to switch my tires with a stock rubicon off the lot. The code flashed again within 2 drives, 20 km. They cleared the code, but stated the pinion factor was set for a 225 tire, not 255, his mistake. He asked me to test it again. Code came back on the 3rd drive, approximately 22 km after they reset everything.

They have scheduled to tear into the jeep next Monday, now that we have proven the tires have nothing to do with the fault code. I haven't tried the above mentioned test to the IAT, but I will this weekend. I have no problem doing this, I used be a Mech Eng. and been rebuilding cars for years for fun. My last jeep was an 80 cj, 305 tbi, scout 44's, full cage, custom tube fenders blah blah blah, all work done by me with my son who was 8 when we started that one. I sold it to purchase this jeep. That old stuff is simple, new stuff with electrical sensors just frustrates me.

Thanks to Shockwave for the advice.

 

Pinion Factor?
That's a new one....I would run from that asshat.

 

Final follow up.

The dealer replaced the coolant temperature sensor. No more problems, who knew eh?

He admits now he didn't believe the oversize tires had any affect on the problem, but was concerned Jeep wouldn't pay for the repair due to the vehicle being modified.

 

So this code is also tripped when the coolant levels are low? Have a 2012 myself and just had this code pop up over the weekend. The level in the reservoir was far below the "Min" line so added some to bring it back to normal levels. Waiting to see if the CEL will clear on its own now. If not, going to reset it and wait and see.

 

Is there a torque value for the coolant temp sensor? I replaced the sensor but it didn't feel like it wanted to screw too far down, ran it and it appears to be working fine but had a small leak after heating up around the threads. Nothing I could find for torquing the sensor and is it safe to use some RTV? Have a new radiator installed back in May due to a seam leak, started popping the coolant temp sensor code, replaced with after market, then OEM thermostat, still had code so changed the sensor today.