Downstream O2 sensor reading richer than upstream

[DemoFly]

As simple as that.

I have a P0432 for inefficient catalyst downstream.

Downstream O2 voltage averages about 0.75 (but of course bounces around like an O2 should)
Upstream 02 voltages averages 0.3v

Can a bad cat make the second O2 sensor read a larger voltage?

 

[accent2012]

Possibly a bad cat, but a leak in your exhaust is more than likely to cause this. Do a visual inspection.

You might also have a bad O2 sensor.

 

[NMBurb02]

The downstream O2 sensor shouldn't bounce around like the upstream. Sounds like a bad cat, maybe combined with an exhaust leak, causing the swings to average higher O2 content.

 

[NMBurb02]

Originally Posted By: NMBurb02
The downstream O2 sensor shouldn't bounce around like the upstream. Sounds like a bad cat, maybe combined with an exhaust leak, causing the swings to average higher O2 content.

Oops, I see now your downstream is giving you rich, not lean. Please ignore the exhaust leak part of my comments.