As a result of a discussion in this thread wether or not fault codes self cancel and recent experience, I thought I'd start a separate thread on this.

So, in that thread the question was raised wether or not you need to reset the stored error codes after fixing the cause.
As it happens I started getting error codes that do not self reset, and yet I have experienced the opposite in my previous 245.

What's going on?
The 1-1-3 my previous 245 threw would self reset by just turning the ignition off and on again.
The 2-3-1 and 2-2-1 I am experiencing since yesterday in my current 245 are more persistent.

I had erased both codes yesterday using the OBD1's reset function. Today I started the engine and within half a minute of idling the CEL lit again and both codes were back.
Hold on...the O2 sensor could not have heated up enough to give useful data within this very short time! Besides, it takes a lot longer for the coolant to heat up to the temp the ECU wants to see before it switches off the cold start program.

So, if I think about it, that would mean that the codes 2-3-1 and 2-2-1 read the "fuel trim" from the levels stored in memory by the self learning feature and not from actual realtime measurements. Those stored levels must have gone outside the permissible window and hence the codes were thrown again regardless.

To test that hypothesis, I performed a full reset by disconnecting the battery for a short while. I then drove the car and by the sluggish way the engine responded to the throttle, I could feel that all trim levels had been restored to factory default.

During that 10-20 mile trip, the CEL did not come back on.
Time will tell if the codes come back...

What are your thoughts on resetting error codes?