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Old 12-10-2016, 04:20 PM
afomenko afomenko is offline
2012 Altima Sedan
2013 Sentra
2006 Pathfinder
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Default 2006 Pathfinder: ECU runs lean on Bank 1 after replacing upstream oxygen sensor

Originally engine was throwing P0420 (Bank 1, catalyst performance below normal).

Replaced catalyst in Bank 1.

In 200 miles I've got PA200: same Bank 1, this time an upstream sensor seems to need replacement.
Shortly after I used "engine cleaner" fuel additive and thought it is a root cause (thread: P2A00 in 2006 Pathfinder after using "engine cleaner" fuel additive?), but looks like this is a wrong path.

Replaced upstream sensor in Bank 1, performed A/F mixture relearning.

Checking dynamic voltage: it will stay around 0.30V at idle (why?!?)

At first I suspected sensor is at fault, but when I run with breaking by engine (artificially creating rich condition): it jumps up to 0.90V, so sensor itslef is good.

On Bank 2, I have steady 0.60V at idle, 0.1..0.95V for the full range under the same engine-breaking test.

For some reason, ECU decides to feed Bank 1 lean, and Bank 2 slightly rich.

Previous sensor was "stuck" around 0.26V, barely moved anywhere from this voltage.
Looks like ECU "got used" to these low values and does not want to go up.

Any ideas?

Last edited by afomenko; 12-10-2016 at 04:25 PM.
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