96hatchy

alright so ive already looked at the CEL code threads but i need to know wut it means. it says catalyst system efficency below threshold.

i put on my bolt on exhaust(didnt even touch the catylitic converter)
test drove my car and it was fine. the next day while i was driving the check engine light went on. it still runs fine.

ohh yea. its a 96' civic cx, all stock except 4 the catback

pdiggitydogg

That code will not affect driving.
Is it an original denso sensor?

You can try just resetting the ecu and see if it comes back. The cat isnt going to be bad...thats ridiculously rare, unless its clogged or damaged

B18C5-EH2

Actually convertors going bad is very common on the 96-00 Civic CX, DX, and LX models because they have a shitty design that has the exhaust manifold and convertor all in one piece, and the manifold cracks where the primary oxygen sensor screws in.

Disconnect the battery cable (or resest the ECU with a scan tool) and see if the code comes back. If it comes back then you'll need to replace the convertor if you want the light to go away.

96hatchy

thanks guys.

actually there is a very tiny crack in the top of the maniflod but i doubt its effecting the o2 sensor

gottabfast

I forget (and I'm not at work to check) did those civics have 2 O2 sensors? P0420 (iirc) is triggered by a problem with the voltage differential between O2 sensors. Pull your O2 sensors and see what they look like...of course I could be wrong and it could only have 1 O2 sensor.

forcefedferio

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gottabfast &raquo;</TD></TR><TR><TD CLASS="quote">I forget (and I'm not at work to check) did those civics have 2 O2 sensors? P0420 (iirc) is triggered by a problem with the voltage differential between O2 sensors. Pull your O2 sensors and see what they look like...of course I could be wrong and it could only have 1 O2 sensor. </TD></TR></TABLE>

yes, they have two o2 sensors, for that code it will most likely be the secondary o2 sensor (post-cat) or the converter itself....most likely the o2 sensor though. Just reset it and if it doesn't come back you're good, if it does then you will have to fix it.

EG8R

Well replace that manifold first. It's cracked which means its letting oxygen in and it's reading a leaner mixture. I say start with that. I'm a Honda tech and I see this alot. The manifold is ****.

JDM R Cooker

will a test pipe throw a cel code ? cuz I have the cel light. da code is p0420. Its a prelude h22 2001. I bought a new denso o2 sensor last summer. Same light n reset the ecu and tried to delete the code.

Crx_Civic

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDM R Cooker &raquo;</TD></TR><TR><TD CLASS="quote">will a test pipe throw a cel code ? cuz I have the cel light. da code is p0420. Its a prelude h22 2001. I bought a new denso o2 sensor last summer. Same light n reset the ecu and tried to delete the code. </TD></TR></TABLE>

YES you will get a light for a test pipe

1990_integra_DA9

po420 is prolly a cat issue.