This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.
A code P0128 may mean that one or more of the following has happened:
Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:
you have all ready replaced the thermostat with the proper temperature opening thermostat(hopefully) and coolant sensor, you say you have to refill the coolant every 2 weeks this indicates that you either have a coolant leak that needs to be checked out and repaired or you are burning coolant which indicates a possible head gasket problem which will have to be checked. a low coolant level will set this code as there is not enough coolant in the engine to get the engine to operating temperature and stay there. these last suggestions is where I would start to look.
Testimonial: "Thanks so much Robert; my vehicle has more than 131,000 miles; I'm sure greatful to get this info, will have vehicle head gasket checked. I've replaced the thermostat twice within 3 weeks and also replaced coolant sensor, still the P0128 code. You are God sent! THANKS!!"
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Where should the temperature gage be normally?
the gage should run no higher than the half way point usually a little below this level unless the car is being run hard or its very hot outside then it will go over the half way point but no higher than the 3/4 mark
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