Downstream Oxygen Sensor Voltage?

[20pontiacvibe03]

Hi, Can anyone tell me what the downstream oxygen sensor voltage reads at idle? I got the P0420 code. I know this generally points to a catalytic converter, but my downstream sensor is not indicating that. As I understand it, in the case of a bad cat the downstream sensor starts to mirror the A/F sensor. My downstream sensor stays right around +/- 0.1 V, while the A/F jumps quickly between 0.1 V and 0.9V. I checked for a exhaust leak using the Seafoam into the PVC line, but all smoke goes out the rear. From what I've read, the downstream sensor should hover around +/- 0.45 V, but I can't find anything that says this is the case for the Vibe. This is a 2003 with 90k miles.Thanks

[bassplayaz06]

according to the diagnostics repair charts, from positive lead on positive battery terminal, and negative lead on the car harness side on the blue or white wire(whichever one is power), and key on on but car not started, the sensor should be putting out 1155 mV. mine read about 400mV which lead to a bad sensor. had the same code, went away after replacing.

[20pontiacvibe03]

Thanks! I haven't checked it with the key on and car off....I'll have to do that...

[bassplayaz06]

what that does is tell you if it's the sensor or a bad wire in the harness, or the ecm. you're trying the right harness, right?

[20pontiacvibe03]

Yes, I'm probing the connector after the harness comes through the floor on the passenger side (blue or purple wire)....