Rather strange numbers. Zero percent O2 indicates that all the 02 in the native exhaust and generated from NOx disassociation is being consumed.

High HC and low CO and NOx could indicate misfires, or a rich mixture. In any event the catalyst appears to be operating very efficiently. If the mixture is rich an efficient catalyst could use all the available O2 including that from NOx reduction to oxidize CO and leave significant HC. CO is relatively more reactive than the last remnants of HC.

Another possibility could be an out of calibration test system. A recent test on one of my cars generated numbers than made no sense, but since it passed, I didnt' bother to engage the proprieter in a discussion.

The M103 engines have been identified as a "high emitter profile" by the CARB. Don't know about the status of the C220 engine.

What were your numbers two years ago?

Duke