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Should I troubleshoot in this order? P0128

4K views 2 replies 3 participants last post by  Renorunner 
#1 ·
I have a CEL illuminated with the code P0128 (Coolant thermostat malfunction). I have checked the coolant levels (hot and cool) and every single fuse in the car. The engine temperature gauge needle will raise almost halfway to "H" during highway driving, and stays just above the "C" when city driving. Is there a smart way to determine and fix what is actually wrong? Or do I just go right for a new thermostat?

How will driving the car with this condition present affect the car? EX: What is going to break/wear out?

Thank You Merry Christmas!
 
#2 ·
Driving with a cold engine with set the ECU to run the engine rich, which in turn will eventually melt the CAT (meaning $$$)..

The dash gauge is not connected to the ECU so is a liniar indication of normal temp..

If the coolant has not been replace in recent yrs, best to flush, replace thermostat and install new coolant...

... Philip
 
#3 ·
Sounds good! I recently had an issue with my t-stat as well. It was opening too early (around 150) then eventually the engine would heat up anyway until the cooling fans regulated the temperature unless of course the a/c was on. This never threw a code, but watching that needle rarely pass a quarter was annoying to see not to mention the loss in mpg
 
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