Hi. Thanks for your responses.

The engine code is AUS.

The post-cat O2 sensor is sitting at o.1v occasionally lifting to 0.4v unless I snap the throttle open. It then fluctuates until the emmisions settle.

There is no resistor fitted to the multi-plug of the O2 sensor on the car. I forgot to mention that the multiplug on the car has 6 wires (the O2 sensor has 5).

The customer has, under interrogation, now told me that the MIL light only comes on on the motorway and sometimes lacks power, other times it's ok. He says the code is for 'emmisions faulty' (I'm guessing catalyst efficiency). He has cleared the code with his own Code reader he got of the tinterweb!!! It has had a non genuine cat fitted too!

I will do a search in archives to see if checking wide band O2 sensors has been discussed.

I can't help thinking that the pre-cat O2 sensor should do something when the throttle is snapped open. I was checking on graph rather than a voltage value.

Any further suggestions appreciated.

Paul.