My CEL came on about 2 days ago and after connecting the scanner, I got this code. I looked it up online and what I found was: either the primary or secondary O2 sensor went bad, or the cat cracked or theres something wrong with it . Lets say for example that the cat is not cracked, then that means that one of the sensors are bad, so I'm guessing just replace those and I'm good right? And if the cat is ACTUALLY cracked, then the only solution would be to get a new one right? I looked at the Honda repair manual and will be doing the visual inspection on the cat since its the only thing I can do rightnow and see what that gives me before doing anything else

FYI: The last time I replaced the spark plugs was about a year ago or maybe a little more, have never replaced the distributor or the rotor in it, the spark plug wires are still the same ones the previous owner had, but the timing belt changed it about less than a year ago. Any thoughts on the problem?

 

just change the o2 sensor and make sure not to get the cheap knockoff versions.

NGK or Denso only

 

I took out the back up fuse and that took the CEL away, at least I hope I should be able to pass the smog in cali but I found the problem of the code afterwards :'-(

Once I change it, imma change the plugs, distributor and rotor, wires, and sensors to have everything good and fresh

 

With only rare exceptions, bad O2 sensors do not throw code P0420.

• Bad cat

• Exhaust leak

It's obviously time to replace the header.

 

^^^plus 1 99% of the time a PO420 is a bad cat and needs replaced.

 

Save your time - there's no way that is going to pass emissions with a cracked header, CEL or no CEL. Fix this first.

 

P0420 means the rear O2 sensor was tested and passed, and then the converter was tested, and failed. The computer will never test the cat if the rear O2 does not function correctly. It will produce a DTC related to the O2 sensor, and will never check the catalyst until it works. That kinda air leak will skew both sensors, and since it uses a comparison of front a rear O2's to determine if the converter works, it failed.

Exhaust leak that is large enough will fail it
Converter is otherwise defective.

 

True but if the rear O2 is that far out of rang it will post a code for the bank 1 sensor 2 O2 sensor not a code for cat efficiency. The way to know for sure is to 1 check the temp in and out of the cat with a temp gun 2 to view the O2 data from the ECU with a scanner that can view ECU data, if the O2 sensors are not responding to increased throttle or the sensors are lazy to respond.

 

The PCM will produce DTC's related to poor response, bias rich or lean for any of the oxygen sensors. It is not out of range because the first sensor will see very similar results to the last one, as oxygen is too high. Any time the computer runs a converter test it looks for these similarities, and if they are too similar, will set the MIL with P0420.

Checking converter temperature is pointless, and is not required by any manufacturer for converter testing.

 

that is one nice crack......

 

It's time to get her some good quality aftermarket header.

 

I wish I could but there are no cali CARB approved header for my trim :'-( only another big *** OEM one. I looked up DC headers since i know those are CARB approved but the only one available is for an EX, I got the LX

 

Or you could buy a complete Dorman manifold/converter setup from Advance.

I paid <$200 for the entire assy, hardware and gaskets included.

 

How would they know if you put an aftermarket in? Do they actually crawl through your car in that much detail?

 

The 96-00 D16Y7 has the cat built into the exhaust manifold, not separate like 88-95 or 96-00 D16Y8 / B16. Therefore, the design of the system can not be changed. Even putting a DC, CARB Legal, header in with an OEM cat from an EX will not pass visual if the smog tech knows what he is looking at. This is especially true here in CA. Like n2xlr8n said, Dorman, Walker, and ATP offer OEM replacement Exhaust manifolds/Cats for your vehicle...all of which are around 200-400 for CA legal manifolds.

 

FWIW, it was a slam dunk, well-casted (shock!) one hour of my time job, and well worth it.

It's a testament to the engineering of these engines that my car could run so well, get >35mpg, and not eat itself due to clogged converter.

I have a like-new running engine now : )

Thanks fellas. Y'all called it.

 

The reason the DC header is CARB stamped for the EX is because the EX doesn't have the cat built into the manifold. You could easily convert your car to an EX exhaust, though, to prevent having to deal with this again in the future.

 

P0420 doesn't necessarily mean the cat is clogged (unless you also have performance and misfire issues as well) it is basically saying the converter is not adequately breaking down the exhaust gases efficiently any longer. Let us know the long term result of the dorman as it has mixed reviews.

 

After Post #3 this was a dead horse you were beating on.