Q: Replacing the left rear oxygen sensor looks easy. What problems may I run into? on 1996 Nissan Pathfinder

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Does a failed rear oxygen sensor affect how the engine runs, or just show the condition of the catalytic converter?
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A bad Oxygen (O2) Sensor will primarily upset the fuel injection system or the computerized carburetor system. The voltage signal from the sensor represents air-fuel ratio. If the oxygen sensor produces a false output (incorrect voltage), the computer cannot precisely control how much fuel is metered into the engine. A rich mixture or lean mis-fire condition could result. Oxygen sensors life can be shortened by contamination, blocked outside air, shorts, and poor electrical connections. O2 sensor contamination can be caused by: 1) LEADED FUEL, which is the most common cause of o2 sensor contamination, Lead coats the ceramic element and sensor cannot produce enough voltage output for computer. 2) SILICONE. Sources are anti-freeze, volatile RTV silicone sealers, water-proofing sprays, and gasoline additives. Silicone forms a glassy coating. 3) CARBON contamination results from rich fuel mixtures. Carbon in fuel coats the sensor. Carbon and moderate lead contamination can sometimes be reversed. Run the engine at high speeds with a large vacuum hose (PCV hose for example) removed and with only unleaded fuel in the tank. This will sometimes burn off light lead and most carbon deposits. The sensor may start working normally again.