What can cause a Check engine code P0128 to come back after it was fixed once. Coolant sensor and thermostat were replaced and no check engine light for about 2 weeks.
P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature.)
Meaning the regulating temperature is higher than the themostat cooling temperature . you may have to replace the Coolant sensor again. or maybe both. Sorry !
I'd check and clean all the grounds in the engine compartment. check the thermostat. make sure you don't have a coolant leak the sensor reads when it is immersed in coolant it won't read steam.
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I have an 01 pontiac grandam it will run fine and idle fine for awhile then it will start to stumble and the rpm gauge jumps around and if you turn the a/c on when this is happening it will stall.
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