I wanted to test and see if my O2 sensor was working properly.
Have had trouble with high NOx. Engine does not have EGR valve. I wanted to measure the output with a voltmeter.
What wire do you monitor for that? It has 4 wires coming out of it. 2 white wires (preheater?), a black wire and a gray wire.
Its a 94 with over 200K on it and so far as I know the O2 sensors have never been changed (or even cleaned). Bought vehicle new.
Many thanks.
grey wire. test with the engine hot. hold the rpms at about 2500 for a few minutes and check that the O2 sensors fluctuate between 0.2V and 0.8V
then wait till the voltage is low and rap the throttle. if the voltage doesn't instantly jump up to 0.9V then that O2 sensor is lazy and needs to be replaced.
most cheap meters don't have a fast enough refresh rate to keep up with the voltage changes though.
at 200k miles your O2 sensors are no doubt performing less than optimal. just replace them all.
also O2 sensors won't help with nox, but will help with everything else.