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Cat efficiency in downstream O2 sensors
Posted to Emissions Forum on 6/2/2017 7 Replies

Greetings all, I'm writing this in response to Steve Wootton's Tech help request today concerning his 05 Jeep Liberty 3.7L oxygen sensors. He was stating that even after replacing the catalytic converters and the downstream oxygen sensors 5000 miles previous, that the Downstream sensors weren't fluctuating like he thought they should. What I got from that was, I think he was saying he thought that they should be fluctuating more like the Upstream ones? Should they be more constant if the catalytic converter is doing their job. I didn't quite understand that and I wanted to clarify this and I was wondering if anybody had any comments on that. Doug.

Here is his tech request: " Verified no exhaust leaks.

When monitoring O2 sensors, upstream fluctuate from 2.7-3.4 volts and change according to vacuum leak or added fuel (brake clean through vacuum hose). Rear O2's seem fixed at 3.3 on bank 1 and 2.8 volts on bank 2 and don't fluctuate like upstream's. Measured temperature of catalytic converters inlet to outlet and found 20-100 degree F increase depending. According to manufacture P0420 diagnostic tree, new downstream O2's and old upstream "may" set the P0420. But the downstream O2's are not fluctuating like the upstream's.

Related Repair History Replaced both catalytic converters 5000 miles ago as well as both O2 sensors. "

Doug Foote
BigFoote Mobile Automotive
Ukiah, California, USA

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