Skip the auto shop - Our mechanics make house calls

Q: Check Engine Light on again after thermostat replacement.

asked by on

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.

A: If the check engine light is coming on and ...

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?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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

Q: Overheating and heater not working

It sounds like you may have a faulty thermostat as well as a bad coolant temperature sensor. If the coolant is not getting to the heater core, then this would indicate a bad thermostat or a clogged heater core not...

Q: Noise at rear tire

The noise you hear may be from an object that got into the tire or you have another problem; if a tac or nail got into the tire, you may hear a tapping noise every time the tire goes around....

Q: Is manifold gasket replacement a diehard requirement for manifold r&r?

The intake manifold gasket can be reused if it is not damaged in any way. The cost of the new gasket versus removing the intake again if it leaks is something to think about. Consider if it's worth the risk...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...