Recently I noticed that my gas mileage has fallen off a bit; maybe as much as 10%. I suspect that after 235,000 miles that my oxygen sensor may have become contaminated. Is there a simple way to test it?
All you need is a volt/ohm meter and a propane torch.
Clamp the O2 sensor in a vise.
Set the scale on the meter @ 2 VDC
Connect the red lead of the meter to the signal wire of the O2 sensor.
Connect the black lead of the meter to the metal body of the O2 sensor.
Apply the flame of the propane torch to the tip of the O2 sensor.
The voltage on the meter should slowly increase towards 1 VDC, and when the flame is removed from the tip of the O2 sensor, the voltage should slowly decrease from 1 VDC.
If the voltage is erratic going up or down, replace the O2 sensor.