Code Reading

  • 4 CYL
  • FWD
  • 144 MILES
Hi, I just had my 2004 Chevrolet Cavalier 2doors 5speed base model read the "check engine" light at the Automotive school where my brother is taking classes to be a "Smog Check Technian and they use a "Genesyst" ODB Code reader(i think that's how you spell it) and it Only shows 1 code which is "P0420A Error Code: Catalyst System Efficiency". If I dicide to just replace the Catalytic Converter will this solve my issue? Or Could it be another part from the Cat is causing and that I should find out? Or Is there any other place or parts that could be causing the Code?
Do you
have the same problem?
Friday, June 10th, 2011 AT 7:41 AM

1 Reply

That's a Genysis scanner which is just the name brand. They are a very popular scanner. To boil a really long description down to a few important points, there is an oxygen sensor in front of the catalytic converter that is used to fine tune fuel metering into the engine, just like they did since the late '70s. It switches its reading between "rich" and "lean" a couple of times per second. Since 1996 models, there is a second oxygen sensor right after the converter that monitors the exhaust coming out. If the converter is doing its job, that second O2 sensor will switch from rich to lean perhaps once or twice per minute. As the converter loses its efficiency at cleaning up the exhaust, less change takes place in the composition of that gas so the second sensor starts switching faster. When there is no change made to the exhaust, both sensors will change from rich to lean at the same rate because they are measuring the same thing. That frequency of the signal is what the Engine Computer looks at to determine when the converter isn't doing its job.

That's how it's supposed to work. While it's true the problem could be with the converter, it is also possible to have a lazy "downstream" oxygen sensor but usually that will set a different code. The converter is the most likely suspect.
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Friday, June 10th, 2011 AT 8:37 AM

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