So I had my catalytic converter replaced in my car yesterday and that night my engine light comes on again. I took it to AutoZone to get a free engine light inspection and they say that it is the o2 sensor that’s downstream from the catalytic converter. Is this common or is it the mechanics fault
Why did you have the cat replaced? The car can set a code that could be mistaken for a bad cat when the O2 sensor is actually at fault. The mechanic didn’t cause the problem but he may not have diagnosed it correctly either. Don’t depend on what the AutoZone guy said - they are not very skilled - take it back to the mechanic and see what he says. O2 sensors are cheap and they wear out.
first of all: The codes doesn’t say “Downstream Oxygen sensor is bad.” It does, however, say that the downstream oxygen sensor is sending a signal that the vehicles computer views as abnormal.
What is the code?
What the code actually is, can depend on how you proceed from here. It could be a legit bad 02 sensor (unrelated to the previous repairs,) or it could be an exhaust leak (which could be related to the previous repairs- depending on where the leak is.)
Also helpful would be if you posted the year and mileage of your Equinox.