now my knowledge on this is mainly 940 based. but bet its the same!

the 02 should fluctuate from less than 0.5v to greater than 0.5v...and with an analogue meter you should be able to see it do it...

they way this stuff works (I think!) is that the engine adjusts the mixture according to a pre-programmed map (x much air at y revs = z petrol)...the air part of the equation comes from the MAF sensor... the 02 sensor then looks at (effectively) how efficient the burn is and feeds back into that loop to 'tweak' the mixture...

I think the MAF sensor works by heating a wire to a given temp and monitoring how much current is required to maintain it..more air = more cooling =more current...but could be measured on resistance i guess

now seems to me the codes probably just indicate the sensor is detecting perminantly rich mixture...possible casues:-

1. blown sensor
2. problem with MAF sensor kiddingthe engine into thinking it has more air than it has...
3. leak in the pipework if its a turbo (air escaping)
4. possibly a dodgy MAF connection where the connection results in miss reading...

sort of makes sense to me...