brendanr279 Posted February 27, 2017 Share Posted February 27, 2017 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. Link to comment Share on other sites More sharing options...
brendanr279 Posted February 28, 2017 Author Share Posted February 28, 2017 Anybody? Link to comment Share on other sites More sharing options...
DaveT Posted February 28, 2017 Share Posted February 28, 2017 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. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted March 1, 2017 Share Posted March 1, 2017 (edited) 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, 2017 by GeneralDisorder Link to comment Share on other sites More sharing options...
GreaseMonkey03 Posted March 2, 2017 Share Posted March 2, 2017 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. Link to comment Share on other sites More sharing options...
DaveT Posted March 2, 2017 Share Posted March 2, 2017 Run it up to normal operating temperature, it should unscrew easier. Link to comment Share on other sites More sharing options...
matt167 Posted March 2, 2017 Share Posted March 2, 2017 Make sure to use a little copper antiseize on new sensor. And am autoparts has a $20 sensor that works Link to comment Share on other sites More sharing options...
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