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Rear O2 Sensor

Having trouble with my 2002 corolla. It has poor fuel economy and sluggish acceleration. The car just sounds like it has a sore throat when it accelerates. Also, i have a P0420 code. Here’s what I have found out so far.

I spliced in a voltmeter to constantly measure the voltage produced by the rear O2 sensor while driving. The Haynes manual reported it should hover around 400 mV. At idle and while coasting, mine is around 320 - 340 mV. The real problem is when I accelerate and when going up hills, the voltage switches over to ~14 volts. Then, once i let off the gas, it returns back to around 320 - 340.

I’m about 99% sure the sensor must be bad, but I also feel like the the catalytic converter might be shot. How could I test that? Can the rear O2 sensor really affect fuel mileage and performance that much?

The rear sensor is there to monitor the converters efficiency…The FRONT oxygen sensor controls the engines fuel mixture. At the 100K mile mark, you should change them both. I would also remove and clean the EGR valve as it could be sticking and causing problems…

You can buy a OBD-2 to USB cable and a diagnostics program and turn your lap-top into a full-featured scan tool. $30-$40 on eBay…

If the P0420 code is the only code, I can 99% guarantee you that you need a new catalytic converter.