Rep Power: 0

My daughter just acquired a 2003 Si from my in-laws. They said the "maintenance required" light was on, but the car failed inspection in MA the day she got it because of the CEL. D'oh. Code was P0134; she was told this is the rear O2 sensor. She took it to a recommended garage, who said alas, it is not the $200-to-replace O2 sensor but the $350-to-replace A/F sensor. I called a dealership to see what price they'd quote, and was told there IS no such part. One website says the A/F sensor IS the front O2 sensor. Hmm.

So, is this garage on the level? If it is the upstream one rather than what she was originally told, is it easily replaced by her? I saw a youtube video for front O2 sensor replacement, mostly involving getting a socket wrench with an open-sided socket...I've replaced spark plugs on an old Mustang, and lightbulbs, air and oil filters, that's about it. But I'm game to try nearly anything that doesn't require precision or a lift.

 
Rep Power: 200

The 02 sensors on any thing are heat sensors basically. Rich they are cold, lean they are hot. Not air fuel, but the same principles except air fuel sensors are just to show you what they read, oxygen sensors are what the car uses to adjust the engine parameters. There is no magic involved, in and out, probably can do it with end wrenches too, the sockets usually aren't a neccesity, are big and bulky, and largely a lot of coin for nothing. And it is the upstream in question here, but the computer thinks the sensor is the problem, check the wires etc before just throwing parts at it. I realize a mechanics was of thought is different than a drivewayer's, but diagnose it first man....