P0420 Error

[AaronM1991]

Took my RX8 out for a drive today and EML came on, I didnt notice any power difference from normal and Im getting P0420 coming up. Is there any simple checks I can do with no tools etc to diagnose the problem? Does this mean that the CAT is knackered?

I have been considering going Decat anyway so maybe this will just speed this process up! What decat pipe would you guys recommend?

Cheers
Aaron

[goodeggbob]

Hi Aaron,if your cat is fubared,then just knock the guts out of it.

[acegeezer]

You already have a decat, as Rob states knock the existing cat's insides out .. voilla

[warpc0il]

https://www.rx8ownersclub.co.uk/forum/v ... 25&t=77699

[AaronM1991]

Thanks for the help.. i know what i will be getting up to soon

[AaronM1991]

Bit of an odd one.. anyone in kent or local with jack/tools willing to help me clear cat? obviously I would compensate for it

[Dan-Lincs]

Good time to buy a jack, stands and a socket set, don't have to pay millions of pounds. Fantastic learning experience too.

[nintenjo]

Strange reading this and mine has the exact same issue starting last week. I have a hi-flow sports cat but I’ll admit it wasn’t the most expensive (JapSpeed)? It’s only about 12 months old and done about 3k miles tops so if it’s gone I am not best impressed, but I do pre-mix so could be the cause...

Annoying as it’s due an MOT next week, and I don’t have time or money to decat it or get it retested with a borrowed CAT. Sod’s law!

How can I confirm this is the cause and not a faulty o2 sensor or poor fitting that’s come lose on a speed ‘bump’ ?

[LeeW]

Woah, hang on. As you’ll see from my thread about selling my OEM cat, don’t smash it out if it’s an OEM!

Where abouts in Kent are you? I have a Japspeed sports cat you can borrow to see if it helps? I got it to get mine through it’s MOT when I was first fixing mine up and it got through fine. It’s not done many miles so shouldn’t be in bad condition still. I also have all the gear if you need a hand changing it over.

[nintenjo]

LeeW - think you have confused me with the original poster (I am not based in Kent, but it’s a kind offer).


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[ChrisHolmes]

Strange reading this and mine has the exact same issue starting last week. I have a hi-flow sports cat but I’ll admit it wasn’t the most expensive (JapSpeed)? It’s only about 12 months old and done about 3k miles tops so if it’s gone I am not best impressed, but I do pre-mix so could be the cause...

Annoying as it’s due an MOT next week, and I don’t have time or money to decat it or get it retested with a borrowed CAT. Sod’s law!

How can I confirm this is the cause and not a faulty o2 sensor or poor fitting that’s come lose on a speed ‘bump’ ?

Contact Scott at Ryan Rotary Performance in Rugby and he may be able to help with getting through the MOT

[LeeW]

No no, I was talking to the OP as he is asking if anyone in Kent to smash his cat out...!

Bit of an odd one.. anyone in kent or local with jack/tools willing to help me clear cat? obviously I would compensate for it

Woah, hang on. As you’ll see from my thread about selling my OEM cat, don’t smash it out if it’s an OEM!

Where abouts in Kent are you? I have a Japspeed sports cat you can borrow to see if it helps? I got it to get mine through it’s MOT when I was first fixing mine up and it got through fine. It’s not done many miles so shouldn’t be in bad condition still. I also have all the gear if you need a hand changing it over.

[AaronM1991]

No no, I was talking to the OP as he is asking if anyone in Kent to smash his cat out...!

Bit of an odd one.. anyone in kent or local with jack/tools willing to help me clear cat? obviously I would compensate for it

Woah, hang on. As you’ll see from my thread about selling my OEM cat, don’t smash it out if it’s an OEM!

Where abouts in Kent are you? I have a Japspeed sports cat you can borrow to see if it helps? I got it to get mine through it’s MOT when I was first fixing mine up and it got through fine. It’s not done many miles so shouldn’t be in bad condition still. I also have all the gear if you need a hand changing it over.

Hi mate, Havent been on in a while so didnt see this! Had my OEM knocked out in the end! Probably should have but just wanted to get something sorted! Im based in Medway so if the offers still there come my MOT time in the summer, i might have to take you up on that haha You local?

[LeeW]

hopefully the silver lining on loosing out on the few hundred quid you would have gotten for your oem cat is that it’s fixed your problem..?

I’m in hurst green now but am always back around Maidstone way as that’s where family are.

[AaronM1991]

hopefully the silver lining on loosing out on the few hundred quid you would have gotten for your oem cat is that it’s fixed your problem..?

I’m in hurst green now but am always back around Maidstone way as that’s where family are.

Yeah the light keeps coming and going but thats because its gutted anyway

I work in Aylesford myself so only next door

[nintenjo]

OK strangely the error has now fixed itself. Could it have been caused by some overzealous premix on my last fillup (think I added about 200ml to a 50lite fill up.. which is more than I would normally do?) Going to get the CAT off in the next week or two and double-check, but assuming that extra oil in the fuel could easily confuse the censor?

[New Duke]

It hasn't "fixed itself" it's just the the PCM can only check cat function during a particular engine mode, usually related to open road cruise at steady speeds.

If you don't drive like this you can't get the CEL.

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[New Duke]

Yeah get the cat off the car asap and have it checked... or just bin it and either get something better or decat and get the CEL mapped out (but only if you decat).

And drive it as little as poss in the meantime. Might be worth using a proper cat to test with as a control.

[Octatonic]

I've also just had this code for the first time. I'm thinking of buying an Essex Rotary Cat or similar if needed. I've read that bad plugs/coils can be a cause of the Cat failing and that if that's the case they will cause any replacement to have a shortened lifespan. I've had no issues connected with starting or reving, seems to me my sparks/coils are ok. Could the failing Cat be caused by something else and how can I confirm it's not the sparks/coils?

[Octatonic]

That error means that the PCM has determined that the cat isn't functioning as it should, based on the input from the rear O2 sensor.

This could be because the cat has failed (or is failing) or it is getting overwhelmed by the nature of the exhaust gases coming through.

Failure of either or both of the trailing coils/leads/plugs is almost undetectable by most drivers, but has a massive impact on emissions, which will overwhelm and eventually destroy the cat.

It also possible that there's a problem with the O2 sensor or it's associated wiring, but this would usually trigger other CEL's in addition to the 0420.

Full description and fault finding for this and all CEL codes here
viewtopic.php?f=58&t=35629

"Launch MAZDA Service Materials"
Switch from Workshop Manual to Troubleshooting in the drop-down
> Engine
> DTC P0420
follow the Diagnostics...

Note that the PCM can only check the cat function during sustained cruise, so you could have had an issue go undetected for months or years, if you don't tend to drive in those conditions most of the time.

[Paul_13]

Did any of the rx8's in other countries come without the secondary air pump?

[warpc0il]

Not that I'm aware of.

Certainly fitted to all North American (US/Canada), Australia/NZ, JDM, UK & European 8's.

Why?

[Paul_13]

Not that I'm aware of.

Certainly fitted to all North American (US/Canada), Australia/NZ, JDM, UK & European 8's.

Why?

Was thinking of editing the pcm as built info to remove the secondary air pump similar to the cruise control mod. But need a pcm flash to compare

[Octatonic]

That error means that the PCM has determined that the cat isn't functioning as it should, based on the input from the rear O2 sensor.

This could be because the cat has failed (or is failing) or it is getting overwhelmed by the nature of the exhaust gases coming through.

Failure of either or both of the trailing coils/leads/plugs is almost undetectable by most drivers, but has a massive impact on emissions, which will overwhelm and eventually destroy the cat.

It also possible that there's a problem with the O2 sensor or it's associated wiring, but this would usually trigger other CEL's in addition to the 0420.

Full description and fault finding for this and all CEL codes here
viewtopic.php?f=58&t=35629

"Launch MAZDA Service Materials"
Switch from Workshop Manual to Troubleshooting in the drop-down
> Engine
> DTC P0420
follow the Diagnostics...

Note that the PCM can only check the cat function during sustained cruise, so you could have had an issue go undetected for months or years, if you don't tend to drive in those conditions most of the time.

It was after an 90 mins long drive and it has only done 20-30mins journeys before that in the last three/four months. So I guess that could mean a failing Cat has caused other problems during that time? What should I look for?

[Octatonic]

Or there is no cat on it at all....