this is kind of weird atleast for me cuz its never happend but if u think otherwise let me know.

what happen was that i had my check engine light giving me codes of P118(coolant sensor) & P420 (catalyic converter)

all i did was change the coolant sensor first since it was only about $30. a very simple task if you got the right tools and ive never even worked on a car before until someone told me its very simple to do.

once i turned the car back on after changing the sensor.... the check engine light was no longer on. NOT EVEN FOR THE CATALYIC CONVERTER.

hmmm..

 

Give it a few days, it might just be the fact that the PCM cleared all codes when it "realized" the coolant issue was no more, and it simply hasnt re-detected (is that even a word?) the cat problem yet...if it doesnt come on after a few hundred miles then you may not have a problem...sometimes the PCM gets things wrong, sensors interact with other sensors for no reason, things affect unrelated things, it happens all the time when computers are involved. Its not a 100% accurate monitoring system by any means...

 

Yea sometimes it just gets a little screwy. My check engine light was on for a few days (yes I checked the gas cap seeing as apparently that's why it's on half the time) and then after a few days it shut off and hasn't come back.

 

when I had my incomming air temp sencor unhooked I had the engine and battery lights come on.
I never did read the error code, i knew it was something to do with that anyway.

I had a nice error on the saturn though, telling me the fuel mix was too rich, when the sencor in the exhaust had burnt out.