Nissan Repair: Nissan Sentra 2000 P0420 Bank 1, p0420 bank 1, nissan sentra

Question
QUESTION: Hello,

My Nissan Sentra 2000 (driven 75k) is getting P0420 Bank 1 code. My mechanic told me the Cat is gone bad and it would cost me $900 with labor if I fix the OEM part. Later, when I check http://www.obd-codes.com/p0420, it seems there could be many causes for this code. I want to make sure that I just don't throw away 900 bucks and then, find out the issue was with O2 sensor or something else. To give you an history, i've changed MAF sensor 3 years back.

Advice please?

Thanks much
Sat

ANSWER: Hi Sat -

Bank 1 I believe is the passenger side. You are correct. I find it hard to think it is the CAT. I don;t think it is the O2 sensor, otherwise you would get a code for that. The exact wording for your code P0420 says "Catalyst system efficiency below threshold".

Might be prudent to have the CAT checked first before condemning it. This checks the exhaust before entering the CAT compared to after, and tells you if the CAT has gone bad.

Hope this helps -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: Thanks Calvin.

A follow up question - how to check the CAT? Can I do it myself? or have to visit the mechanic? If I ask the mechanic to do it, then, what should I expect that he should/would do to thoroughly check and know/measure?

Thanks much.
Sat

Answer
Hi Sat -

Yes. Best thing to do is see a competent mechanic. There are 2 main tests:

1. Test the emissions before entering the CAT and after. Thresholds should match manufacturer's specs for carbon monoxide removal. If not, the beads inside are saturated, and the CAT needs replacement.

2. Test for excessive back pressure. Sometimes the inside of the CAT collapses and will cause power and fuel robbing back pressure in the exhaust system.

Unfortunately the devices used to test this are expensive and far and few, so best thing is to take it to someone you trust and test.

Hope this helps -
aloha
calvin