Oxygen Sensor was replaced but engine code and light still come on

Many months ago I had my oxygen sensors replaced on my car. However, the check engine light keeps coming on with the code for faulty oxygen sensor. The mechanic thinks it says this because of a wiring problem and that I should get the electrical system fixed. Does this sound right? If so, how extensive would the work be? The electrical system in the car seems to work with all other functions except my radio.

After market radio, and or remote start etc.?

Your car may be different, but on both of my Subarus the O2 sensor code that showed up was occuring because the catalytic converter was not operating properly and needed to be replaced. The problem may not be with the O2 sensor at all. Has your mechanic explored this possibility?

Just because an O2 code is set does not necessarily mean the O2 is at fault. There could be one or more other reasons for that code.It sounds like your mechanic wild guessed, lost, and is now defaulting to the wiring because he does not have any idea.

You might consider providing more info on the car along with exactly what code was set. An O2 code could be pre-converter or post converter. My assumption, right or wrong, is that it’s the latter.

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I gather that O2 sensors and catalytic converter issues can be tricky to diagnose.

But when your mechanic starts blaming the wiring, the wiring harness, or “the computer”… it’s a sign to me, at least, that he’s out of ideas. You need to try another mechanic.


I agree with @ledhed75 - this should be a straightforward diagnosis, you mechanic appears to be in over their head. I’d find another one.

Well . . . ?!

Is he capable of diagnosing and repairing this problem?

From what you describe, the answer might be no

Because if he was able to do so, you wouldn’t be here asking for help

Seems to me the underlying reason(s) for the oxygen sensor fault codes was never properly diagnosed in the first place

All fuses related to the oxygen sensor(s) good?

No obvious wiring problems, such as rat damage?

How about you tell us which exact code(s) you have?

Not the description, just the code itself

Such as P0130

I expect that the next stab in the dark will be “bad gas”. That (or “the computer”) seems to be the default diagnosis for a lot of clueless mechanics.

What does your mechanic say his scan tool is saying about the sensor performance? Are they providing expected data? The sensors are showing varying readings? Or nothing? So they are “broke”?