Got a CEL with my 2012 MCS yesterday, and whipping out my Scangauge reveals the P0136 oxygen sensor fault. Well documented here, of course a common one.
I'll get it serviced and move on.

However: I thought I'd try resetting / turning off the CEL just to see if it would re-trigger (and to further check out the sensor: is it really dead, or was just confused for a spell?). Tried that with my Scangauge, it just shut off. Weird.

Pulled out my Garmin ecoRoute dongle and Garmin Mechanic software. Got the P0136 code displayed, indicated "reset", it thought about it...and came back. The light's still lit.

So it looks like there's something in the OBD for my car that's set to resist having the light reset by the usual means. I've used my Scangauge on other cars to reset the light, worked like a charm (esp on my 2007 CX7, it liked to spit off its gas cap, eventually recalled with a better design).

Thought this was weird, for sure. It's storing the codes anyway...a diligent search of posts didn't reveal anything similar. Was there an OBD software change recently that prevents these tools from working?

 

Did you try and reset it with the engine running with the scanguage?

On my N14 JCW I can reset error codes with the engine running with the scanguage. However, if I this on the N18 it doesn't work, and the scanguage goes blank.

I read the FAQ on the scanguage page, and this is a common problem on some cars, which do not allow a reset with the engine running. For most of these it can be reset with engine not running, but the key in the running position. I tried this and it worked for me.

Try this. Switch engine off. Unplug scan guage. Push the start button without the clutch depressed, so it is in the engine running position, but without the enigine going, in this position the aircon should be running etc. Plug scanguage back in and wait to communicate, then scan and clear code

Works for me

 

*Yes*, the engine was running.

Great feedback, thanks! I'll give this a whirl.

And of course...after a couple of restarts, the CEL light went out. I'll be ready for next time, though.

Thanks again.