View Full Version : Q: How to test an O2 senser

05-28-2008, 09:14 PM
Is it sad that Im asking you guys about how to work on my lancer cause the mitsu board, if its not an evo, they wont help you. Really this place rocks, now that 2k is gone its a great place :lolhittin Just kiddin...or am I? Im'a update my profile one day. I still have the stx but it needs a tranny job cv shaft for me to unrice the exhaust :bigthumbu and the engine needs some seals and gaskets. BUT on to my question. My lancers been throwing the PO421 code which means either my cats bad or the o2 behind it is. I learned in high school how to test an o2 but I cant remember. :rubs crystal ball: " O dear celicatech members of vast knowledge, show me the way to test an o2 senser"

05-29-2008, 08:09 PM
Are you telling me that noone knows how to use a multimeter to test the voltages at the senser? C'mon guys

05-30-2008, 03:09 AM
You can't really check the sensOr with a multimeter for that code, the signal changes too fast.
You can check the heater part, but that's not your issue.

You should see a relatively smooth signal from the sensor after the cat, but you need a scan tool to view it [or an ocilloscope].

05-30-2008, 03:38 AM
I just found out that my car had a recall on the cat and a pcm update so Ima call the dealer tomorrow