P0420 after cat replaced

Hi,

Need to find out what my next step is. Got a Honda Prelude, 1999, with
180K highway miles. I just replaced the cat since the engine light came on
a few months ago, plus my emissions/smog test was due soon. Even the dealer
told me the light is a likely indicator for a new cat, AND it's OK to drive
it until I'm due for my registration renewal.

So I replaced it two weeks ago. I was also informed that my cat had a
built in O2 sensor, hence it was expensive. So I drive it around a little
bit but the light didn't go off. So I decided to fork the money over to at
least get the emissions test and find out what else is failing. All passed,
except the MIL because the light is still on.

Tech also said do not disconnect the batter because that resets the
computer, and it'll push me about 1 week of driving since the computer has
to be in it's pattern (whatever that means). highway driving is not enough
because it's reading "high" speed? Dunno why that matters.

The emissions test center said I have another sensor at the top that most
likely wasn't replaced. Is this true? More than 1 cat sensor?

My registration renewal is due next week. The MIL light turned off. But it
has been on-off in the past few months also. I'm wondering if it's off due
to increased stop-n-go driving in the city recently, and the computer is
in its "normal" pattern. I'd like to avoid having to go for another test
to see if it'll pass.

What do you folks recommend?

Thanks in advance.

 

yes, you definitely have two sensors - one just before, one just after
the cat. code P0420 is "Catalyst System Low Efficiency". if you have
the same code both before & after replacing the cat, you can be pretty
sure it's the sensor.

 

"goldenset" wrote

Any excuse to replace a cat is ok with me, as long as you don't get another
cat.

 

notice he never said the light was reset at time of cat replacement.
and the o2 sensor is not built in, it screws in just like the rest.
they should have cleared the codes and done the idle learn
procedure.
Chip

 

"chip" wrote

I know exactly what he said. He and you are talking about cats. I'm
suggesting perhaps he get a dog instead. Dogs learn "idle" very quickly.

 

the cat replacement wasn't done by a dealer. rather a small mom/pop shop.
now i wonder if the quality was even there since the time it took was too
fast.

i did want to go to the dealer to ask a buddy to reset it for me. but
that's when a local smog shop said don't (explained in my earlier post).

all in all, the light finally went off. I've been driving in the city a
bit in the past two weeks. light went off, and never came back on. so i
decided to get another smog test today given the mil was the point of
failure last time.

and.... it passed. maybe it does take some time for the system to
recalibrate itself w/o resetting the codes?

 

what did you replace it with and where? a Honda cat? the oxygen sensor isn't
"built in", its screwed in just like any other o2 sensor.