Air/Fuel Ratio Sensor?

[Rickmaan]

I've been researching possible problems to clear the CEL on my '01 Legacy GT and one of the items I found mentioned is an "air/fuel ratio sensor" that commonly fails. Is this just an O2 sensor or is it a mass air sensor or something else?

[StatGSR]

whats your cel code say it is?

[Rickmaan]

I was told by my mechanic the CEL decoded as "misfire on #1 cylinder", but I have new plugs and wires, and the shop tested the coil and said that was good. This wouldn't be the 1st time a CEL code didn't accurately point at the real cause, and the symptoms (rough idle, fluctuating idle) seem to match what I read about the air/fuel ratio sensor. I'm just not sure what sensor that refers to. If it's not the sensor I'm afraid it might be the infamous head gasket issue, so I figured I change the sensor 1st since that will be a lot cheaper.

[Huffer]

The front O2 sensor is the A/F ratio sensor. What was the exact code, not the "decoded" version from your mechanic. 1 digit off can result in a pretty interesting parts replacement process.

[rougeben83]

p0171/misfire bank 1? Yeah it's the front 02 sensor (aka the wideband 02 sensor/afr sensor)...ask me how I know :wink:

[decke48]

po301 is number 1 cyl misfire.

[Rickmaan]

Thanks for the info guys. I don't know the actual code the mechanic read from the ECM, only that he told me it was a misfire on #1. I'll get the O2 sensor and hopefully that will fix the issue.

[Rickmaan]

Sorry it took so long to update this topic (6 months isn't that long is it?), but I replaced both O2 sensors and the CEL has not returned yet, knock on wood. Maybe I only needed to replace the front one, but with over 100k on the car I figured it might be time to replace both of them.

BTW; I asked the mechanic after my previous post and the code was 301, misfire on #1. Thanks to rougeben83 for the tip that actually got rid of my CEL! :grin: