2013JKU error code and message P0128 "Thermostat Rationality".

TomDabb

TomDabb

Member
Jeeeep - yea, initially it was perfect - 160 degrees at the registers - now only 10 days later - barely an heat, kinda warm at slower speeds.
I can see clearly both the rubber and aluminum pipes. No bends or kinks. Thanks


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TomDabb

TomDabb

Member
Thanks Petersen1988 - no leaks found or loose of coolant. Overflow remains always dry and Level under rad cap full when cool.
We reverse cleared the heater core with a chem flush - this work perfectly for 10 days. I'll check the pressure/temperature sensor too - thanks - I'll let everyone know as I go thro this frustrating mess.
Btw 2013 JKU


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CharlesC

CharlesC

Member
There is one right behind the glove box. Remove the glove box and run your hot/cold knob and you should see it move the lever. This one is very easy to replace if not functioning right. The drivers side is a PITA to replace, matter of fact I had to take it in and have it done. Sucked$
Refer back to my original post for the drivers side. Worth checking-


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TomDabb

TomDabb

Member
CharkesC - pass side blend door actuator confirmed working fine.
What I fine interesting is that when I measure the surface temperatures of both pipes going to the heater core, first under the hood on both aluminum pipes then again but inside and just behind the actuator the temp diff seems significant. Under the hood reads 150 to 170 degrees yet inside they read only 70 to 80 degrees.


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CharlesC

CharlesC

Member
TomDabb said:
CharkesC - pass side blend door actuator confirmed working fine.
What I fine interesting is that when I measure the surface temperatures of both pipes going to the heater core, first under the hood on both aluminum pipes then again but inside and just behind the actuator the temp diff seems significant. Under the hood reads 150 to 170 degrees yet inside they read only 70 to 80 degrees.


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That is weird, you should have one pipe that is hotter than the gates of hell that is under the hood and to the core and the other that is not on the return.

You have auto climate control right? Did you check the drivers side blend door? If I'm not mistaken, I think the drivers side is the one that controls your auto control from AC to Heat and keeps the temp that is set. If it is stuck in the direction of blending to AC it will only blow cold. Sounds like that might be your issue🤞


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TomDabb

TomDabb

Member
Thanks - not automatic climate control on my Sport, all manual. I haven't gotten to see the drivers side yet. I removed the easy snap in place lower dash cover under the steering wheel.
Like you said, it looks like a PITA to get at. Try it tomorrow when the suns up.


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TomDabb

TomDabb

Member
2013 JKU w/89 k. So in an effort to try again with a twist. I hope I'm correct. On 11/25 I report weak heat yet again.
So reach out and reading a boat load, in came down to doing a heater core flush with heated white vinegar followed by 10 minutes for tap water straight from a hose nozzle minimal pressure. Lastly prime with distilled water, reconnect the two heater core rubber tubes (at the ends of the aluminum pipes). Start it up, rad cap off and run until it reach approx 100 degrees at the cap. 1/2 Closed the cap and revved it until all the air was gone.
I'm happy to report full heat 165 degrees at all registers.


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jeeeep

jeeeep

Hooked
TomDabb said:
2013 JKU w/89 k. So in an effort to try again with a twist. I hope I'm correct. On 11/25 I report weak heat yet again.
So reach out and reading a boat load, in came down to doing a heater core flush with heated white vinegar followed by 10 minutes for tap water straight from a hose nozzle minimal pressure. Lastly prime with distilled water, reconnect the two heater core rubber tubes (at the ends of the aluminum pipes). Start it up, rad cap off and run until it reach approx 100 degrees at the cap. 1/2 Closed the cap and revved it until all the air was gone.
I'm happy to report full heat 165 degrees at all registers.


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hope it holds...

Did you have the front end elevated up on jack stands to bleed the cooling system?
 
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