Originally Posted by unclebuck48
Hi all, my check engine light came on. I took it to Auto Zone, they hooked up there computer and the code P0420 came up Catalyst System Efficiency Below Threshold (Bank 1). Auto Zone said it was probably the oxygen sensor before
the catalytic converter, so I replaced it. 3 days later it's back on, so I replaced the plugs. 2 days later it's back on
. This time I took it to Kragen Auto, they hooked the computer up and the same code was there, he reset my computer thru his handheld computer, 10 miles later it's back on. Ok, so I look online, OBD-codes.com and it says "the oxygen sensor downstream after
the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs)". So, should I purchase the oxygen sensor after
that converter instead of the one I already installed before the converter? Any help would be appreciated.
I have a 98 LX with the same P0420 problem. Have been confused by
many opinions on the web. I took the chance not to replace
the CAT but to replace the following:
1. Primary O2 sensor or before CAT - (Autozone) Bosch 13075 $97.41
2. Secondary O2 sensor or after CAT - (Autozone) Bosch 13071 $89.84
3. A new set of spark plug wires (Genuine Honda) $80.51
4. New distributor cap (Genuine Honda) $24.04
5. New rotor (Genuine Honda) $19.72
6. 4 new spark plugs (Genuine Honda) $12.73
Total cost: $324.25 (including tax in TX)
The CEL light went away after these new parts were replaced.
The car also passed the smog test the day after.
Like many Honda owner, the P0420 haunted me for almost 2-1/2 years as the
CEL comes and goes. I did not find any forum on the web that could provide
a "real" solution. Some opinions are misleading and simply waste
my time. I took pictures during the whole process and I will try to
set up a web site to help those who have the similar problems.
I also cannot believe why you replaced just one. If one goes bad,
the other one goes bad at the same time. The one that I removed showed
that the secondary sensor was in a really bad shape, worst than