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

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: Thermostat and odometer

You have two separate issues going on here. The odometer readout not showing the mileage is likely a faulty instrument panel or the wiring related to this. The thermostat functionality is separate from that of the odometer. As you may...

Q: I started my car this morning and went to put it in drive. As soon as I took my foot off the brake to give gas it shut off completely.

This may be related to a couple of possible things. There is a component called an idle air control valve that monitors the air intake as it is mixed with fuel prior to being injected into the engine at low...

Q: Looking to buy this vehicle and they say it needs o2 sensor replaced

Hi there. Without a proper inspection being performed, there is really no way to determine the extent of the needed repairs. If there is a stored code that points to the O2 sensor, that does not mean that the sensor...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.