After driving around 40,000 miles with my CEL constantly being on, it suddenly turned off I'm so use to it that when it turned off this morning, I thought something was wrong with my car.

 

my car did the same thing, was on for like 5,000 miles and then just went off for like 3 days and then came back on again!

 

you mean your CEL caused by your test pipe or somethin else?

 

high flow cat

 

your code hasn't happened since last 40 cycles, which means you start your car, turned your car 40 times or so (standard is 40 cycles, mitsu, I don't know the specifics) without that code happening again.

This only happens, ex: you had p0300 code cel light on, but for the next xx cycles the p0300 didn't happen (mis-fire). So the cel light turns off.

eh...

 

put some antifoulers (extension) on your o2 sensor, that way you can run your high flow cat or test pipe wihout the CEL

 

turn your key to the on position and make sure the bulb didnt blow. After 40k it might have.
Just another guess.

 

I've had that happen. I blew off one of my intercooler clamps and got a code and I didn't bother resetting the ECU or disconnecting the battery. The next morning, my CEL was gone, but it was still stored in memory.

 

That might be the case. I'm going to see in a second.