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Old 11-28-2019, 03:07 AM
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smj999smj smj999smj is offline
Master Enthusiast
2006 Pathfinder
2003 Frontier King Cab
2003 Frontier KC SVE 4x4
Join Date: Jun 2012
Location: Prospect, VA
Posts: 1,849

The rear oxygen sensors do not effect engine management; they are only catalyst monitoring sensors used by the ECM to make sure the upstream converter is efficient, so it's not them. The front oxygen sensors are actually air/fuel ratio sensors, which operate a little differently and can be hard to determine if they are working properly outside of the ECM triggering a code. They are expensive and usually last a long time, but should be replaced any time the upstream converter is being replaced and most converter warranties specify that proof of replacement is required to enforce the converter's warranty. P0174 occurs when the system is too lean, which means the ECM will counter will adding more fuel. Since it is bank 2, which is the driver's side, the first thing I would check for is an exhaust leak on that side at the flange gasket between the exhaust manifold and the upstream converter. I would also look at the manifold flange for signs of cracks where a look could occur. There have been a few reported cases of cracks developing at that particular area on these vehicles and perhaps while working at replacing the converter, it caused this crack to open a little wider? If you had a bank 2 catalyst code prior to the replacement, it may have caused that, as well. A disconnected vacuum hose or dirty/bad MAS can also cause lean system codes, but usually you'll see codes for both banks, not just one.
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