Check Engine Light and Codes

I admit to total ignorance right off the bat.

The CEL on my 1999 Chevy Prizm came on so I went directly to Pep Boys. $99 later I sure wish I had known about the Auto Zone free reading of codes, especially since what the code revealed was a problem with the catalytic converter, which work Pep Boys do not do so I’m still driving around with the light on. BTW, the code seems to be p420, with (2) 02 sensor muffler on the next line, whatever that means.

I’ve tried to keep maintenance work up to date but at 185K I’m not surprised when something like this happens. I’d like to know a little more about what to expect in the way of fair repair costs.

In researching catalytic converters I was alarmed at how expensive the part itself is, but intrigued by some listings at under $100. This last little part was only one element in what looked like the whole exhaust system, which costs hundreds of dollars more. Is the catalytic converter only one “module” in this whole apparatus? Does the expensive “whole nine yards” include a muffler?

Thanks in advance for any info/insights/observations.

I advise you to first read a bit more on the P0420 code, which you can do over here:

Then follow up with this link to see how P0420 applies to your Prizm in greater detail:

Then check back with your questions.

The person who scanned the check engine light, at Pep Boys, should have looked at the oxygen sensors’ voltages while he was doing the scan. We’ll only know if we have sworn testimony, from him/her, to that effect. Auto Zone, etc., will probably, only do a code scan…no voltage scans. You could ask for a fuller scan; but, I don’t think you’ll get one.

Thanks - I’m reconsidering the whole problem. Last time the CEL came on it was the sensor.

Thanks - those are excellent links and have restrained me from rushing out to get the first catalytic converter anybody will install for me. I’ve dope slapped myself for not asking about the oxygen sensor.

My $ 0.02 worth, it’s one of the O2 sensors. Some cars have a trigger to turn on the CEL at 90k for the O2 sensor.