See my post about the low cost code scanner OBD2 software on the general interest forum:

https://mitsubishiforum.com/forum/ge...e-codes-47530/

Using the iPhone app gave me the oxygen sensor voltage at the time an error code occurred and also plotted a graph of the voltage against time. It is very interesting but now I have to find out whether it is normal for the voltage to fluctuate from 0.1 to 0.85 volts in a severe oscillating wave. It looks like a sine wave almost with a cycle length of 2 to 5 seconds. This is occurring on the oxygen sensors on both banks but it is only bank 2 that is giving P0173 errors with the mixture trim approaching -25%. So other posts on P0173:

https://mitsubishiforum.com/forum/mi...-1999-a-47108/

 

This link says that these regular swings in sensor voltage from 0.1 to 1 volt are normal:

Help with o2 sensor voltage - S-10 Forum

 

There is a very detailed article about O2 sensor technology in Wikipedia but it does not discuss the voltage fluctuations seen in these graphs. However it does discuss the reasons for O2 sensor failure. Normal life is 100,000 miles (160,000 km) but it can drop to 15,000 miles. See:

https://en.wikipedia.org/wiki/Oxygen_sensor