My wife's 2001 4 cyl. LE is showing the good old P0420 (catalyst system efficiency below threshold Bank 1) check engine code. In checking the output from the O2 sensor to the ECM I found 3.5 volts. I was expecting between .4 and .7. I disconnected the sensor and checked it independently. I found the output from the sensor to be around .7 volts - much better. A check at the engine side sensor connector found 3.5 volts at the contact that corresponds to the sensor output. Where is 3.5 volts coming from. I suspect a short between the sensor connector and the ECM, but how do I find it. Or, what else could it be.
HELP!

 

This might help:

http://www.autoshop101.com/forms/h37.pdf

 

Thanks Toyomoho,

Excellent article. More info is a wonderful thing. I'll give it some more thought but now I think the sensor system is working properly. This would make me think that the cat. converter is bad. Makes sense, the car has 125,000 mi. on it. Probably time to retire the converter.
Thanks again
Jim