Was I Just Ripped Off Catalytic Converter Or O2 Sensor

Question: Was I Just Ripped Off Catalytic Converter Or O2 Sensor,
The “check engine” light on my 1996 Saturn SL2 came on about a week ago. I decided to take it to Auto Zone for a free test. It pulled code P0140. The guy told me that it could be my catalytic converter, but if my car was running fine and if I didn’t notice any rattling, it was likely my O2 sensor.

So, I take it to the shop, and they tell me it’s my catalytic converter. I asked if they were sure it wasn’t the O2 sensor, and he said, “It’s definitely the catalytic converter. You need a new one.” I found it strange that he didn’t offer any explanation, but since I’m incredibly stupid and know nothing about cars, I let them go ahead and put a new one on. It was not cheap.

The very next day, while I’m driving home from work, my “check engine” light comes on again. I take it to Auto Zone, and this time, it’s pulling code P0133. Doing a little research, it sounds like the O2 sensor!

So, here’s my question: Was it my O2 sensor all along? My car was running fine. No rattling. No “rotten egg” smell. Normal fuel economy. Did they just say it was my catalytic converter because they knew they could get more money out of me?

I realize that it was a dumb move letting them fix a car that was running fine, but it doesn’t really seem like they actually fixed whatever was causing my “check engine” light to come on. Help?

Best answer for Was I Just Ripped Off Catalytic Converter Or O2 Sensor

O2 Sensors should be replaced along with the Catalytic Converter. Old sensors and new converters do not always get along. The shop should have at least suggested replacing the sensors at the same time.

But keep in mind, all Autozone does is read a code, which does not tell you what the problem is, just where to start looking for it. And they guy at Autozone using that cheap $80 code reader isn’t a mechanic, he is a salesman. That is why the scan is free, because you get what you pay for.

P0133 is a code for “Oxygen Sensor Slow Response Bank 1 Sensor 1” which may mean the sensor is not switching rapidly enough.

P0140 is a code for “Oxygen Sensor No Activity Detected Bank 1 Sensor 2” which means the sensor is not responding at all. But this is the downstream (after Cat converter) sensor, not the sensor in front of the converter that triggered the P0133 code.

Smells like a Cat problem to me but then, I haven’t seen the car and you can’t replace parts just based on a code or you will get it wrong almost every time. There are tests that have to be done to confirm the correct operation of components. Have Autozone clear the code and see if it comes back. It may not.

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