Q: Computer reads an issue with the oxygen sensor on a Subaru Forester 1999 2.0 Turbo. What is the problem?

asked by on October 20, 2016

computer reports oxygen sensor after diagnosis what is the problem

My car has 97000 miles.
My car has an automatic transmission.

Your 1999 Subaru Forester has pre and post catalytic converter oxygen sensors. The pre-converter sensor optimizes fuel trim while the post converter sensor monitors the efficiency of the catalytic converter. A failing pre-converter sensor will degrade vehicle MPG performance. Although a code may set that "identifies" one of these sensors that does not always mean the sensor is "bad". For example, the post converter sensor may show up in a Diagnostic Trouble Code but the real issue is an actually failed catalytic converter. Similarly, a variety of causes, such as sulfur contaminants from leaking valve stem oil seals, and even a failed fuel injector, can cause the pre-converter sensor to fail. Although you could replace the sensor, it will fail as well unless the underlying malfunction is addressed. For a comprehensive diagnosis of the trouble code, and repair, of this issue feel free to contact YourMechanic for assistance.

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