Q: Check engine light with a code about insufficient temperature P0126 to the engine.

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Check engine light with insufficient coolant temp to the engine code P0126. Temp gauge reading below normal. Took it to a shop and replaced with a new thermostat as the obvious solution. Drove off and an hr later, same issue, same code. Checked and the thermostat is working fine but the check engine light is still coming on and now in cold winter temps the car is having a hard time starting, once it heats up it's ok but the check engine light stays on. Is there another sensor were missing or what could be the issue now? Thank you

My car has 154000 miles.
My car has an automatic transmission.

Hi there. The coolant temperature sensor (CTS) is not working correctly. The sensor is sending a signal that the engine is already warm and when the engine first starts up, it needs more fuel a rich mixture to produce more heat until the engine is hot. When the engine is hot, the fuel backs off making the fuel trend more lean. I recommend replacing the coolant temperature sensor. If you need further assistance troubleshooting your cooling system, then seek out a technician, such as one from YourMechanic, that can assist you with your vehicle.

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