Engine light on Codes P0420 and P0430

[Laurence Dunn]

Hi all, Codes P0420 and P0430 showing. I've got 128,000 miles on my car and recently replaced the O2 sensors all 4. My setup is Long Tubes, Cats X pipe, stainless exhaust and Pypes bombs. Everything else is standard, engine is in good shape, new plugs, coilpacks. On the emissions test I had a hard job getting through, but it passed eventually, I've been told my cats are basically worn out. Has anyone else had this problem, and did you get new cats, if so which ones are best? Or was there something else I should be looking at?

cheers Laurence

 

[07 Boss]

Well if the cats are wore out you might try some cat sims. I use them without cats and get by my obd readiness test with them, no codes. I think I got them from BigDaddies.



I had to get the 90* ones because of where they are located on my mid-pipe.




They're like the spark plug anti-foulers that some people use but these actually have a cat substrate in them.

 

[GlassTop09]

Hi Laurence Dunn,

Yes the cats may have gone bad, but there are several other issues that can cause the cats to seem that they've failed as well.

I'd suggest to do the following before replacing the cats to ensure that the cats are bad:

1.) get car smoke leak tested on induction side, on exhaust side (from end of midpipe--not tail pipe--to exhaust manifolds where the O2 sensors live) & full EVAP system smoke leak test to find\fix any air leaks. Just get the car fully smoke leak tested to ensure that there isn't any external air entry bypassing outside of MAF........the far & away fastest, easiest & most thorough method to use for a modern car.......

2.) test the EVAP CPV (canister purge valve) to ensure that this valve isn't leaking when it is closed (main control valve for ECU to use to control EVAP canister purging......if it is leaking while NC (normally closed), the engine is getting excess air entry thru the EVAP canister\leaking flex line off EVAP canister bypassing the MAF so ECU cannot account for this excess air in its calcs thru the front O2 sensor feedback thus the rear O2 sensors are picking this up post-cat & increasing their rear-to-front O2 sensor switching rates).

3.) check\test all O2 sensors for proper operation.............

To keep it as short as I can, the P0420\P0430 Cat Inefficiency DTC's are due to too much free O2 getting passed thru the cats (cats use free O2 to oxidize HC & CO & hold free O2 created from NOx reduction as well as ECU switching the front O2 sensors to replenish some free O2 as well to be used for HC & CO oxidation (fancy word for burned up......products of incomplete combustion).

The ECU checks the cats for 1.) their ability to fully consume free O2 & 2.) their ability to HOLD free O2 sent into them to be used for HC & CO oxidation.

Good cats will pass very, very little free O2 thru them when they're working well thus the rear O2 sensors will switch very, very little to not at all vs the front O2 sensor's constant switching rates while in CL operation.........these rear-to-front O2 sensor switching rates are what the ECU is counting to determine if cats are still efficient or have lost their efficiency. The ECU has a programmed cat efficiency threshold limit set that the ratio calc'd from this switching algorithm the cats have to stay below........once they cross this threshold these P0420\P0430 DTC's will be set.

O2 sensors only are designed to detect for the presence of O2 & nothing else so this is why the suggested work be done 1st to rule out any of these failures before cat replacement......you might be replacing good cats & having new cats show to fail if all this isn't done prior replacement to prove that the cats have failed.

These things costs far too much to be playing the parts cannon scenario...................

The rest is up to you.............

Hope this helps.

 

[Laurence Dunn]

Great thanks for such a quick response to a Mustang brother in need, I'll have a good look and plan my next steps

 

[john knox]

i put cats from amazon on my wife car after p0430 it blow substright out tail pipe, all stock under hood= 2 new cats +4 new 02 sensor, it had pypes exhaust cut off failed cat tiged new one on https://www.amazon.com/MAYASAF【2-Un...68-81f6-ed447b090be9&pd_rd_i=B09HH4VLP9&psc=1