Hi, guys.  I have only very basic experience with multi-meters, and even less with car sensors. 

 

2002 Forester S, OBD II code PO037, downstream O2 sensor.  I located the sensor in the catalytic converter, unplugged the wiring harness, and I have a multi-meter.  The multi-meter is set to the OHMS setting that does not have a number, it just has a strange symbol and "volume" type symbol.  I think this is the generic OHMS setting, correct?  

 

There are four wires to the sensor, two gray, two white.  I probed the both pairs of wires, gray to gray, white to white, and the multi-meter did not react for either pair.  The multi-meter reacts when I touch it's two probes together, so I know it's working.

 

Did I accurately test this O2 sensor?  Does it mean it's faulty and needs to be replaced?  Or what should I do differently to test it?

 

Thanks.

Anybody? 

With an ohm meter - when the probes are open circuit, that is infinity ohms, so the display will have some symbol to indicate open loop, or over range, or similar. When you touch the probes together, it should display a very low number, depending on the sensitivity of the meter and or range it is set to, since that is near zero ohms. It's normal to get a few tenths of an ohm in that case.

 

I don't know what the common readings are for that sensor, without looking in a factory service manual. Note - not all sensors can be fully tested with an ohm meter.

That's a heater circuit failure. The sensor is bad. Get a new one. Happens all the time. Heating element burns out in it.

 

GD

Edited March 1, 20179 yr by GeneralDisorder

I concur. Once the heater circuit code comes up, not even worth checking. Just replace it. Don't go nuts with a wrench on that thing. Take your time. Soak with penetrant. Try again. Repeat the process. Don't want to strip that O2 bung.

Run it up to normal operating temperature, it should unscrew easier.

Make sure to use a little copper antiseize on new sensor. And am autoparts has a $20 sensor that works