ECU clear it's own codes?

[phoonTy]

A couple months ago, the LGT set a P0420. Over Easter weekend, I did the spacer fix for the rear O2, but at the time, it didn't clear the CEL. Flash forward to yesterday... My wife and I finally broke down and bought an OBDII scanner since both our primary drivers are OBDII. I plug it in to the LGT and it says "NO CODE." The CEL light has been off for a week or two now. I figured the code was still stored in the computer, and the scanner would read it, even with the CEL off, but it didn't show up.

I've never heard of a self clearing ecu. I haven't disconnected the battery since Easter. I was driving around, the CEL went off, and hasn't come back since. Does the Subaru ECU work this way? or is it symptomatic of some other electrical issue?

[Huffer]

The ECU is running hundreds of tests every time you drive. It will clear a code if it passes the test.

A CEL usually only shows up if the tested item fails 3 cycles of tests.

[phoonTy]

Cool. I try to learn something new everyday, and this qualifies. :lol:

Thanks!

[decke48]

if it doesnt see a problem for 40 drive cycles it will shut the light off itsself