slowpoke-7

Hey, so I got the p0420 code (catalyst below threshold) and looking to get a new cat. I'm not going OEM from Honda b/c they have clearly bumped their head on something to charge $800+ and then add labor on top of that...so I'm looking at a few aftermarket cats. I want to go with a hi-flow METALLIC substrate b/c they last longer and provide more power & better flow. But it seems that these type of cats are for OBD1 vehicles only (the metallic substrate cats). My car is OBD2...so my question is...if I buy the one I'm looking at and then use the CEL fix where the secondary o2 sensor port is (after the cat), will I still throw a code? This is kind of the same situation for those who run a test pipe except that the hi-flow cat is filtering the gases...the reason it would still throw a code, though, is b/c the flow is too much...so if I get the CEL fix, it should cure the problem, right or wrong?

Thanks in advance for your help folks.

ReDHaTcHyGuy

what car is it for?

NACvicSi

Yes if you fix the CEL then it will work fine. The car has no idea what kind or even if there is a cat on.

lostforawhile

have you checked the rear O2 sensor? they go bad all the time and if it goes bad the computer thinks the cat is bad. it measures before the converter and after the converter, so bad data will give you that code

slowpoke-7

2000 Civic Si

No I haven't checked the o2 sensor...wouldn't that throw a different code though? Either way, I plan to replace the cat with a hi-flow cat and if I need to, the o2 sensors as well.

lostforawhile

if the rear sensor is bad, the computer doesn't always know it failed, it may not be completly failed, but it's not reading right, if this happens, and it happens a lot, the computer will be getting a bad reading from it and think the converter isn't working. it's measuring the O2 content after the converter and comparing to the O2 content before. A lot of people get scammed by shops for this reason, it's nothing but a sensor, but they sell a replacment converter

slowpoke-7

Well I had a good cat on my car prior to a straight up trade for my aftermarket exhaust system for a stock exhaust system...the tech that did the swap switched out the cat with the other guy and ever since then, I got the the code and the exhaust system itself is a #FAIL! So I'm pretty sure its the cat so I'm going to switch that out and later switch out the o2 sensors (not sure if they are the original ones or not so it may be time lol).

lostforawhile

that sensor is screwed into the cat,if he swapped it, there's a good chance he didn't swap sensors, but just unplugged it and swapped everything, that sensor may have been bad before he swapped it in, they almost never get changed, just the front ones normally get changed, thats nealy always the reason you get that code. With an ODD2 engine, the engine parameters are so closely controlled that the cats almost never go bad. the main reason for a cat failure is an engine that is running far too lean or far too rich.

slowpoke-7

Well I didn't throw a code before the swap and if that is the same o2 sensor, then that would mean the cat is indeed the problem, right? lol...either way, the cat is getting replaced, I just wanted to know if the CEL fix would prevent from throwing a code.

lostforawhile

the cat may be fine, but the sensor screwed into the cat that was swapped may have already been bad, so when everything was swapped, you got a bad sensor, if you have a meter that will read miliamps, you need to connect it to the output wires of the sensor, then warm the engine up, then try revving the motor with the meter attached, if the voltage doesn't change or changes very little, the O2 sensor is bad.

slowpoke-7

I'll try it, but I'm still going to replace the cat with a hi-flow metallic core. And then later BOTH o2 sensors...really just wanted to know if I got the CEL fix if it would keep my car from throwing a code as stated earlier.

Thanks though dude.

lostforawhile

that was millivolts sorry, typo