P0420 after cat replaced

Question:

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.

– Hide quoted text — Show quoted text -> 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.

Response:

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?

Response:

"chip"   wrote >> 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 >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

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.

Response:

"goldenset"   wrote > 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

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

Response:

>"goldenset"   wrote > 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 >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

Response:

- Hide quoted text — Show quoted text – > 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.

Response:

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.

Response:

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