Hello. I've recently purchased a 2000 Echo with just over 100k miles.

The check engine light came on last week and I attempted some fixes (change air filter, clean MAF sensor) and reset the codes before having them read.

The light came back on after about 15 miles so I had Auto Zone check it. It returned two P0420 (those are zeroes) codes which stated on the machine that it was an inefficient catalyst issue, or something near that. They suggested to replace the catalytic converter, but some reading hinted at trying the "downstream" O2 sensor first since it could send the same code and it's cheaper.

I replaced the sensor today and cleared the codes only to have the light come back on before I'd run 15 miles again. I had Auto Zone check it again and it still returns two P0420 codes.

Before I give in and shell out the funds for a catalytic converter replacement, I wanted to check here and see if anyone has any other suggestions on what it might be. It's bad enough losing $130 on a sensor, but I'd sure hate to drop a load on the converter and that still not fix it.

Thanks in advance.

see attached

Many thanks. Lots of good information there. Wish I could test sensor 1 myself to determine if it's faulty. It does give me another place to look, though.

Is the rest of that manual available online somewhere? Looks like some good, thorough documentation. I'd like to get my hands on it.

Hello. I've recently purchased a 2000 Echo with just over 100k miles.

The check engine light came on last week and I attempted some fixes (change air filter, clean MAF sensor) and reset the codes before having them read.

The light came back on after about 15 miles so I had Auto Zone check it. It returned two P0420 (those are zeroes) codes which stated on the machine that it was an inefficient catalyst issue, or something near that. They suggested to replace the catalytic converter, but some reading hinted at trying the "downstream" O2 sensor first since it could send the same code and it's cheaper.

I replaced the sensor today and cleared the codes only to have the light come back on before I'd run 15 miles again. I had Auto Zone check it again and it still returns two P0420 codes.

Before I give in and shell out the funds for a catalytic converter replacement, I wanted to check here and see if anyone has any other suggestions on what it might be. It's bad enough losing $130 on a sensor, but I'd sure hate to drop a load on the converter and that still not fix it.

Thanks in advance.
It's the CAT CONVERTER, It needs to be replaced
Pm me for price if your interested

Thanks for your response. I'm doing some other diagnositcs still, so I'm not ready to buy the converter yet. Thanks for the offer, though.