Is there any way to check the O2 sensors with a volt/ohm meter? The factory manual says to use an oscilloscope but I do not have access to one. I get a 0420 code (catalyst efficiency below threshold)But I would like to make sure it isn't just a lazy sensor. It is my understanding that this car has 2 Cats, 1 at the exhaust maniflod and 1 in the pipe ahead of the muffler. How would I know which one has gone bad or do you just replace both (expensive). By the way the emissions sticker says this car approved for CAL & OTC OBD II certified.
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You can check the O2 signals with a voltmeter but voltmeters are very slow, they don't react fast enough to really give you a clear picture as to how the sensor is operating. That's why they suggest an oscilloscope, which is very fast.
I suggest you check out this article our emissions expert wrote about the p)420 Code, he deals with these issues everyday and is on of the leading emissions experts in all of California. http://repairpal.com/OBD-II-Code-P0420-Toyota
Thanks for the reply. I think I have solved the P0420 code problem. The car was always driven real easy almost never exceeding 2500-2700 RPM. Every time I reset the CEL It would return within 2 days. I reset the light, took the car out on a 2 hour 65MPH w/o overdrive (3100 RPM) run. I haven't got the code for almost 2 weeks now.
Thanks for the reply. I think I have solved the P0420 code problem. The car was always driven real easy almost never exceeding 2500-2700 RPM. Every time I reset the CEL It would return within 2 days. I reset the light, took the car out on a 2 hour 65MPH w/o overdrive (3100 RPM) run. I haven't got the code for almost 2 weeks now.