Originally Posted by HumanMode

Update for those interested.

My mechanic has gone over the car with a fine tooth comb and all sensors and mechanicals are working as they should.

After a reset or OBD clearance, all the error reports return (but without specific codes), the engine light returns and the car goes into a limp-home mode that is very drivable - just sluggish.

Not sure if this is relevant, but mechanic noted that in live reading O2 sensors on right were steady, but sensor on left gave wildly erratic readings. Swapped sensors, and left still played up. Tried sensors on another mercedes and they were fine.

The mechanic thinks the problem is a compromised ECU. Local tuner and Australian tuner concur based on the reported action, but local tuner won't touch it in case of bricking the unit without the original file to flash to the ECU.

The car was tuned by the local Mercedes dealer probably 2010-ish, before I owned it. I will check with the dealer, but it has since changed hands.

So what do I do?

I think my only option is to talk to Needs Wings about an ECU replacement?