swanny

Hi Guys,

I have owned my s2000 for 6 months and since buying the engine light has been on with the code p420 bank 1 cat inefficency below threshold! the car has a replaced standard cat on, and has recently had both 02 sensors replaced in a hope to turn this bloddy light off, I have also tried putting a spacer on lambda primary and still after literally 18 miles driving after code is cleared the frickin light comes back on. Ive been told that aftermarket cats cause these codes, I dotn want to buy an oem one as planning on selling car, is there any other tricks or suggestions to get rid of this code/engine light, many thanks

Sebring AP1

Buy defoulers. Get two and you'll be fine.

postman

Don't buy defowlers. For starters using a defowler on your upstream sensor could be very bad for the engine. The issue is the cat. Buy a Honda one, can get used ones cheap on here. Selling a car with a known issue like that is shady anyways.

BLAQ&GREYs2k

You dont pur the defoulers on the upstream sensor, and I agree you never should. The defoulers are for the downstream sensor. The computer compares a/f ratios from the upstream and the downstream sensors and throw a P0420 code when the two read similar. Just buy a test pipe with defoulers, unless you have the money to go to honda and spend 1,000$ on a cat? Makes no sense to me.

Billman250

After my experiences with stock cats coming apart, breaking o2 sensors and clogging to point of power restriction, I wouldn't recommend one to anyone.

Defoul the secondary o2 for your CEL, AND to protect it. A broken cat can't break an o2 with a defouler on it.

I also recommend ANYONE with 80k miles or more put a defouler in your stock cat, just to protect the $265.00 secondary o2.

AP1Driver

I've had this issue forever as well! I gave up after a new cat and 3 new downstream sensors. Mine will go off sometimes for days, and then stay on for days. Been doing it for over a year since I tried out a test pipe for 2 days that I hated after 2 minutes.. Replaced the cat with a magnaflow, thought that was it; new OEM bolt in: same issue. I wonder if the wires are so sensitive that during installs they get frayed or broken inside, or loosened inside the plug itself.. Like I said, I gave up as stated... Doesn't hurt a thing the way it is.

I thought about welding in an anti fouler but would need another 02 as the hole has twisted threads that will ruin the o2 when I unscrew it. Unscrewing 3 heat welded o2s will do that. It barely bit enough to hold when I screwed it in.

dln78

Get the the defoulers, drill one so the o2 sensor can fit. Get some steel wool, and fill up the first defouler that connects to the catalytic converter or test pipe with some steel wool. Make sure not to stuff it too much with the wool or else you'll get another cel(mil) code p0137 (o2 sensor circuit low voltage, bank 1 sensor 2), which in my case not enough gases were getting through to the o2 sensor because I over stuffed the defoulers with too much wool. Screw in the second defouler that's been drilled to fit the o2 sensor on top of the first one, then screw in the o2 sensor and there you have it. At least that's what worked for me and I drive an 07 with the extremely finicky o2 sensor. Good luck to ya!