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Discussion Starter #1
My 2009 Dodge Nitro (4.0 liter v6 sohc engine 4x4 lhd) check engine light is on with a P0128 code.
I feel confident the ECT sensor is bad. The car heater puts out hot air almost immediately and the car never overheats and runs great. Can anyone tell me where the sensor is located on my Nitro?
Also, can it be replaced without draining all my coolant?
Also want to know if there is a bench test I can do on the sensor.
Any help is much appreciated.
 

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Khaki Nitro Nut
07Lifted,4X4,6sp-man,3.7L
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30,638 Posts
May not be the sensor.
P0128 = Coolant thermostat - coolant temperature below thermostat regulating temperature. Possible causes; Mechanical fault.
The T-stat is stuck open.
If that is the case you have quite a chore to replace it.
There is a how-to in the KB section.
https://www.nitroforumz.com/threads/how-to-thermostat-replacement-4-0l-engine.39314/
Quote from the how-to, post 18
"temperature sensor. It is located right on the thermostat housing."
All the tests I see are for the wiring not the actual sensor.
 

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Discussion Starter #3
Thanks for your reply. I really have a hard time believing that the thermostat is stuck open because if that were the case I would expect it would take longer for the engine to come up to normal operating temperature. After starting the car I can drive about 2 miles down the road and it’s putting out hot air from heater and the temperature gauge at that point it’s reading normal. I never overheat either. I want to go after the sensor first as I’m assuming it to be an easier job, not sure. Any additional thoughts are welcome and appreciated.
 

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Khaki Nitro Nut
07Lifted,4X4,6sp-man,3.7L
Joined
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30,638 Posts
The DTC says the error is generated by an engine run "time" to reach operating temperature. If it takes more then the "set time" to reach 185 Deg, the DTC will set. Unfortunately it does not say what the time is...
It does mention this code may set on very cold days.
2 trip fault, and 3 good trips to reset.
It also mentions low coolant/air in the system, may cause this to set.

The heater get its coolant directly from the engine, bypassing the T-stat. So cabin heat may not be greatly affected.

The strange thing to me is the temp gauge. The computers get the same reading as what the gauge says. If it is sitting at 1/2 then it is at operating temp. The question remains; How long does it take to get there?

One test they mention was to watch the gauge temp(via scan tool) and also set a thermometer in the radiator. Comparing the 2.
Without a scan tool, you may be able to guesstimate the gauge needle and thermometer.

Is the outside air temperature reading on the cluster accurate? If not, then that can also cause the fault.
 

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Discussion Starter #5
the outside temp is correct. interesting thing though, the CEL came on after the first really cold day I've seen thus far this year.
 
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