CEL, P0420 on RX8 series 1 2005
 

Hi all

I have looked through the forums and have been able to get some good info on this CEL code so far, but wads after more clarification please.

My IOBD device shows the code as P0420 Catalyst System Efficiency Below Threshold Bank 1

I was travelling at 90Kmh on a freeway when it threw the code. Pulled over checked the IOBD and reset it.

So far it has not come back on yet. that was today though.

I recently had my coil packs go out on me and it I am concerned the cat got damaged. The packs were replaced along with the plugs.

I am chasing advise on whether this could be cat or oxygen sensor or both? I am aware that coils can cause cat failure if too much fuel gets down into the cat.

If so , is there a good cat that I can use that is not OEM as the Mazda ones are very expensive. How do you distinguish between cat and oxygen sensor problem?

Cheers

Ice

It is easy to test if it's the cat, just drop the front end and look in. P0420 will only be thrown for a cat failure if the catalyst elements are gone.

See this prior post of mine for what you might see inside the cat: https://www.rx8club.com/series-i-tro...2/#post4592977

Thanks

So you mean if the cat is not clogged or cracked it maybe something else like the oxygen sensor.

I don't have access to a car hoist so getting the exhaust apart is going to be difficult. I would have to take it to Mazda and they charge like a wounded bull.

I drove it again for another hour after resetting the code and it has not done it again, but does that mean nothing in that it may throw it again at anytime?

I guess I will only know once the cat is looked at properly.

It may be just the cat. Aftermarket cats are hit and miss, meaning some will last most wont. Due to the extreme high heat of our engines most cat will burn too hot and come apart fast. It may be the O2 but usually those throw a different code i believe dont quote me tho been a long day lol

In my case I was getting PO420 for quite some time with my car running seemingly fine to then getting problems with lack of power getting progressively worse at high RPM.
The front half of my cat was mostly gone except for 1 egg shaped piece and the back half was intact but clogged.

I guess the only way to find out is to have the pipe apart and take a look inside.

I tell you what bugs me though. My coil packs died.......does this mean I automatically have buggered my cat? I just cannot believe they would make an engine that cooks a cat just because coil packs die. We do not get the extended warranty in our country either.

Is there any chance it will just go away...lol How much does a reasonably good cat cost fitted?

Your wasting valuable time on this if it is the CAT and it's clogged your doing damige to your engine. Get it off the car and check it out to confirm yes or no wether it's clogged worry about what els it could be once you confirm the point at hand.

I can't say for sure but I don't think it takes a long time. If you imagine what a misfire does by basically causing a blowtorch effect of raw fuel being ignited in your exhaust pipe under already extremely hot conditions, it's easy to see how it could go bad quickly.
I was almost sure there was nothing wrong with mine at first because it seemed to run fine and only started to run bad after several weeks of trying all kinds of easy remedies to no avail.
I replaced mine with a BHR midpipe over a year ago and have until August to get it inspected.
The OEM cat here is in the neighborhood of $1400 U.S.

Fwiw my '04 GT had less than 19k miles on it when the cat went bad from only 1 bad coil & plug.

Either way it sounds like $$$

Will drop it off and have a look. I can get an after market cat for $800

If it is fried don't drive with it on or you'll be looking to buy a new engine and CAT.

How do I tell if it is fried without taking it off? The car drives perfectly , plenty of power and no hesitation whatsoever. I will need to get to a car hoist so will have to drive it.
They need a warning light on the dash........it would read "your CAT is fried, get out and walk"

Research your choice thoroughly as emissions requirements vary depending on location.
Some aftermarket cats don't last.
If you have to put off buying a proper cat, you can gut it in the meantime if you have to drive it.

One way many check it is to drive it at night and look under it to see if it's glowing.
Another way is to jack it up and hit it to see if the strata is broken up, it will rattle, but won't if it's clogged.

So if it is gutted doe sit still pose a problem with causing engine damage.

I need to understand what is meant by don't drive it if it is fried? Why? Do you mean if it is clogged or simply not there having been blown out the back....

I will need to get it foxed properly, but don;t want to cook my engine on top of this cat issue.

By the way

which part is the CAT, the first bulge after the engine or the second bulge. If it is the first bulge in the pipe what is the second one for?

Thanks

A clogged or melted cat will damage the engine by not allowing the exhaust through, forcing backpressure into the engine, causing the damage. Installing a catless midpipe eliminates that possibility.
Gutting it allows the exhaust to flow freely, but will not pass emissions testing.
You also have to be sure there are no chunks blocking the exhaust beyond the cat.
There is a DIY here on gutting cats.

The first one with the oxygen sensor is the cat, the other is a resonator to help quiet the exhaust like a small muffler.
If you get a midpipe, a resonated one would be quieter.
My BHR midpipe has one.