[tomj76]

Thanks for the replies.

I've used the A-B terminals in the past with a short circuit for the Field Service Mode, but I was not aware that a 3.9k ohm resistor would initiate another mode. Very helpful.

However, I don't think the fuel trim data is valid at all when the PCM is operating in open loop mode, while O2 sensor is cold (it doesn't even generate a voltage when it is cold). It usually takes about 2-3 minutes for the O2 sensor to get hot enough and the PCM to switch to closed loop mode. Time to get some real world data.