Check engine light

My 03 VW Jetta has a Mal Ind Light issue. It keeps coming back on. I have a great mechanic who gets his kicks by figuring out german car problems! But this one is a mystery. The code is always the same-Engine Coolant Temperature. Previously I had a P0101 Mass Air flow code but then my car broke down and the fuel pump was replaced (but that was a couple months ago). My car seems to run fine and when he checked it out–couldnt find anything not working correctly. What is it?? Could it just simply be the sensor? or something much more involved?

Don’t know about you, but Read the post in 2nd opinions on My 230 SLK benz, check eng lt problem. Problem was wrong fuel. Is your VW Jetta suppost to have premium? does it? if so maybe a bottle of octane booster or techrolane additive may do the fix. Good luck.

Is the temperature gauge reading in the correct range? You could have a thermostat that’s stuck open or a fault CTS (coolant temperature sensor).

Common problem. Replace the coolant temp sensor.

Even though the sensor checks out fine when your mechanic looks at it. It will occasionally throw a fit and trigger a check engine light.

They had a bad coolant sensor on that range of years. As I recall they redesigned it twice. I believe the original one was black, that was replaced with blue and the blue was replaced with green. Regardless, make sure you get the most current one.