Q: Check Engine Light on again after thermostat replacement.

asked by on January 25, 2016

I got my car serviced about a week ago for a thermostat problem. The issue was fixed, but I was going to take my car in for a smog check and the check engine light came on again. The light hadn't been on for a few days after the fix. I took the car in to the smog check and the technician ran a diagnostic test. His reader indicated it was a thermostat problem. I just want to know why the check engine light came back on after the thermostat was already replaced.

If the check engine light is coming on and a code like P1217 is in the computer then the computer is seeing an overheat conditions from the coolant sensor telling it your engine is overheating. This can be caused by a defective coolant sensor, radiator partly clogged, fans not working, thermostat or internal engine head problems. The system should be checked with an infrared temperature probe to see if the temperature of the engine is close to that the computer is seeing from the coolant sensor. If the coolant temperature sensor input to the computer is within about ten degrees of what the infrared tested is reading on the outside of the sensor then this would be okay. The problem may be somewhere else in the system and would need further diagnostics to check if other components are working properly. The fans will need to be working along with the water pump pumping coolant through the radiator and the radiator cooling the engine as designed. I recommend having the vehicle inspected by a certified mechanic to diagnose your Check Engine light and come up with any repairs needed.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Leaking transmission fluid - 2004 Ford Crown Victoria

Hi and thank you for contacting YourMechanic. There are 3 places for transmission leaks to go - externally to the ground, through the module vacuum tube, and into the coolant system through you transmission cooling lines. Since there is...

Car drives poorly with heavy fuel consumption and poor transmission

Hi and thanks for contacting YourMechanic. First, with the dirty cooling system, you would need to perform a coolant flush and replace the thermostat and radiator cap. This will help with the overheating issue if you are still experiencing that....

Do you have to do a factory reset on my car ?

Hello. If everything was done correctly then it should start right up. If it is not getting spark or fuel then I would check the crank signal. If the crank sensor is not sending a good signal then the computer...

Related articles

P0116 OBD-II Trouble Code: ECT Sensor Circuit Range Performance Problem
P0116 P0116 code definition Engine Coolant Temperature (ECT) sensor circuit range performance problem What the P0116 code means P0116 is the OBD-II generic code that indicates the engine control module (ECM) ECT monitor has read that the ECT sensor range...
P0302 OBD-II Trouble Code: Cylinder 2 Misfire Detected
P0302 code definition Cylinder 2 misfire detected What the P0302 code means Most vehicles have either 4 or 6 cylinders. Each cylinder...
P2086 OBD-II Trouble Code: Exhaust Gas Temperature Sensor Circuit Range/Performance Bank 2 Sensor 2
What What the P2086 code means? P2086 is an OBD-II generic code for the exhaust gas temperature sensor circuit signal is out of range for bank 2 Sensor 2 to the engine control module (ECM). This means the sensor signal...