1999 Mazda Miata P0420 code

I;ll try to break it down for you. The downstream o2 sensor can't be the problem and I'll tell you why. P0420 sets when the downstream o2 sensor switches TOO RAPIDLY indicating the catalyst has lost it's efficiency. A bad o2 sensor NEVER switches too rapidly. They switch too slowly, or they intermittently stick or they stop altogether. Now, they may have wanted to replace it for good measure(i would too) but it's not causing the P0420. This is why it's best to allow them to replace the sensor, because your warranty would be intact. Now , because you didn't allow them to replace it, they may not want to honor the warranty(although they should) So, give them a call or take it back and give them the opportunity to fix it. If your supercharger isn't driven properly(overdriven, or underdriven) then it can definitely cause a lean condition that will damage the catalyst. I wouldn't warranty the Cat with a supercharger installed either, to be honest. No, there is no recommended way to "tweak" the ECM. Im sorry for the bad news, but that's the way it goes with aftermarket parts installed for increased performance. They don't mesh well with the OEM parts.

Thanks for the info. Here's some more input tho clarify my situation; a) the cat was damaged well before the supercharger was installed so it wasn't a factor in that failure, b) the P0420 code was there from the day that the cat was replaced by the dealer (I saw it on the dealer's tester, and then had it verified at Autozone), c) the car is well out of warranty (120K+ miles) so that isn't an issue. After a bit more researching, I discovered that, yes, I can't realistically "hack" the ECU - bummer, and d) the 'charger is running the "stock" JRE pulleys so not over/under-driven. Now for the "good" part...I ran the car today to work with my laptop plugged into the OBD2 (via an ELM interface) and logged my trip into work. What I saw was that the voltage from the downstream sensor was oscillating fairly rapidly - almost in synch with the upstream sensor. There was a short period when the downstream signal seemed to "plateau", but only briefly before oscillating again. My trip to work is only about 20 min with about 10 min of highway driving. Discover more Forum fuel OBD Given that, I have a few more questions; Is the nature of my morning commute contributing to the problem? Is my cat "toast" (remember, the CEL was on before the 'charger was installed), did the dealer screw me? I saw a "little black box" on the 'net that claimed it could replace the downstream cat and trick the ECU into thinking that it was still there by mimicing a proper signal. It is intended for those folk that put in a straignt pipe in place of the cat pipe (ostensibly for racing) where there no longer is a downstream O2 sensor. Does anyone have any experience with this? I this a viable solution?

Its not a viable solution, in my opinion. Cleaner air seems to be the best solution. Did you stipulate the pricing for the cat? Many times the consumer may tell the shop that "I want the cheapest cat, cuz they're all the same". If that's the case it's not true. Cheaper cats can cause you problems. If they installed a quality OEM converter, then you should have turned right around and went back to let them take a closer look at the vehicle. Now, that said, I've heard from reputable sources that heating a converter up can cause the catalyst to work again. Perhaps your short drives to and from work aren't allowing it to warm up . So take it for a nice long highway speed drive and see what happens. Perhaps that's all it needs.

Nice statement eh! Did the dealer screw me? Screw off! and take your yuppy want to be tin can hotrod with you!

To "Darkrooms"; thanks for your help. I askd for, and was charged for an OE replacement cat. I'll be sure to go back and find out what I really got. You're probably right about the short trips. I did lots of highway miles this past weekend without the CEL coming on. Guess I'll have to take the long way home. To"Jeff"; I came to this forum to get some intelligent, useful technical information from trained professionals, or helpful enthusiasts. Your response indicates that you are neither. I never asked you to like, or condone my choice of vehicles and frankly I don't care if you do, or don't. That, sir is your problem entirely.

You're response indicates that you are exactly like the sterotype! Slag the dealer and look for a little "magic" black box that'll trick the cars pcm into keeping the check engine light off!

Comp, easy, easy, man. If it's not blatant, why go off like that? He didnt' mean anything byit, really. Dont scare everybody off, man! To the OP: You should only need to heat up the converter once. Once it's up to temp once, it should start working and then keep working. Resume your daily short trips and see if it helps.

Why go off on him! Because something needs to be said! I think the webmaster needs to put a sticky post up about how no technician slagging off any kind will be tolerated! I know we kinda went into this last week but the message isn't getting through. Mosts people's dissatisfaction with dealers stems from a poor sales experience ie paid too much etc or they're just wanting to complain about things that require re-engineering versus repairring on new vehicles or they didn't want to wait for the manufacturer to release the revised parts or software to the dealer to have there vehicle repairred. Who they are pissed with is the service dept at a dealer. The techs can only repair what they can repair, simple as that! I highly doubt the dealer installed an aftermarket converter when it should have had a Mazda replacement for his warranty but does he really think that's a techs fault! No! Enough with the bashing off any kind on this site towards repair facilities, You people are here for free guidance and advice from professionals! If you want to be ignorant you can be left to your own demise, A bunch of po'd consumers sitting around yelling at keyboards and no one getting anything repairred until somebody with the same vehicle and sympton as you hits on the lucky repair on the roulette wheel and shares it with you! That is assuming that it's the same repair that yours requires. This is a site for guidance! I don't need to hear about somebody's negative experiences with a repair facility to repair there vehicle. I only need to know what has been attemptted if anything? was it performed correctly, what parts were used etc? I don't need to hear " I think I was ripped off" We don't even have the vehicle in front of us and I think most of the time we're pretty accurate. That should be grounds enough to be respectted!

I agree 100%. How about if I post a PM to the webmaster about it. Maybe he'll post a "PLease read this first" post at the top of all the forums or something. I'll let you know if he says anything about it. It'll work out.