Last few days its been VERY cold. Currently -33 and when I first start the truck I get this code. Says T-stat rationality...but why would it be tripping this code? Is it related to the ambient cold temps?

Just curious.

 

P0128-THERMOSTAT RATIONALITY
The coolant temperature does not rise by a calibrated amount over a calibrated amount of time.


Possible Causes
COOLING FAN
COOLANT TEMPERATURE SENSOR
THERMOSTAT

Do you plug block heater in?

-33 (((brrrrr))) that's cold...it's 75 here in Southern Cal today.

 

just a hunch but i dont thinnk it would have that many miles without being plugged in haha

 

Plugged in all the time. It did this last winter when it was cold too but only a couple of times. When I clear the code, it does not come back til it sits overnight. Could be the t-stat. Might have to change it as its original factory part.

She be cold up here eh.

 

is this a good time to mention is slightly above freezing over here, dont get me wrong it was -25 monday night but its beautiful today haha

 

put a winter front on it. The ECM is not seeing the temps rise in a set time and trippin the code. with temps that cold it takes FOREVER to get to required temps. close that sucker off and it will rise in time. if it is only happening in the severe cold like you have now, a t-stat isn't going to cure it. if it happens when its warmer out (like above 32) then a t-stat would cure it cause its stuck open and not warming up fast enough. its just too dang cold and the ol girl is tellin ya she don't want to go anywhere.

 

I do have a winter front on the truck. The entire grill and the lower openings are closed off. I am thinking its just because of the severe cold. I will see what it does this morning as it went from -33 to -7C right now.

 

Hey Scotty, here is what I use: go to the dodge dealer and ask for p/n 82208646. Its a vinyl/cloth under hood winter front with 4 flaps for air control. The truck warms up fast and with the flaps closed, really holds in the heat. Last weekend we were sledding and it was -19, truck sat for 5 hours and when I came back the water temp was still at 138 degrees according to my Insight and blew warm air as soon as I started it.

 

I had that code several times right after I bought my truck in 08. The first time was on a cold/rainy45 deg. November day, when I was bringing my truck home from having the Boss plow mounted. On that day it understandably warmed up quicker than normal. It then threw the code several more times. As timing would have it, a recall notice/flash came out for the issue, which seemed to have corrected it.

 

No CEL or MIL today. Truck warms up real nice and throws heat so I feel confident it is not the t-stat. Now that I think about it...each time this code popped, I had set my high idle [1200 rpm] and when I came back to the truck, the CEL/MIL was on. Maybe when its cold and the high idle is engaged, the temps that the ECM expects are not within its parameters.