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Old January 31st, 2010, 14:13
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Ecomike Ecomike is offline
NAXJA# 2091
Join Date: Dec 2006
Location: MilkyWay Galaxy
Posts: 15,264
Re: Testing Jeep O2, Oxygen sensors

Originally Posted by blistovmhz View Post
Hey Mike, I just wanna confirm with you, that the sensor wire VOLTAGE should fluctuate while the engine in running.

I'm checking my 90' xj's O2 sensor, and I get the 14V on the heater wire to ground, 5V on the signal wire to ground with engine off, power on.
But, I continue getting 5V when the engine is running, with no voltage fluctuation. Amperage seems to increase over time...
I also noticed that there is about 0.2-0.4V on the ground, to ground...?

Can I safely assume my o2 sensor is pooched? (God it'd be nice if it was...)
If you have the engine running, the O2 sensor is connected properly to the harness connection, and you are probing the 5 volt supply and the ground, then it sounds like one of 2 possible problems.

The first to check and fix is the ground. It should read less .05 Volts from the O2 sensor ground wire to the battery negative post. You made need to run a new ground from that harness to the battery. I had to run about new sensor grounds on mine to get the ground wire standing voltage down to less than .05V, if you fix the ground first, and still have a steady 5 volts, then replace the O2 sensor as it it the most likely suspect.
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