Re: P0420 and P0430

New member. First post. Original 944 owner and now have acquired from a friend a 2001 2.7 Boxster with 115k miles and many problems. This car passed emissions last year but dealer told former owner the cats were failing. Have tracked down and remedied most problems. Last action was to replace all oxygen sensors based on fault codes(P0150 & P1130 and age), clear all remaining codes due to battery disconnect and attempted drive cycle. Drive cycle has not reset all readiness indicators (secondary air system remains at fail) and fault codes P0420 and P0430 have now appeared for the first time since my ownership. At present these are the only engine module codes. I am seeking wisdom from those wise in the ways of 986. First question is, in the presence of known good oxygen sensors, what component failures could produce these codes, other than converter failure? i.e. where should I look, test and certify before spending big on replacement converters? I have scanned the first 150 pages of posts looking for information and understand the issues of “jeff in VA” (Check Engine Light=> 2 new cat converters) but issues raised in his post appear to remain unresolved. Second question concerns available replacement converters if they are needed. I see ads for Porsche, DEC, USA and Davico. Is anyone experienced with these brands? Comments? Any and all input will be appreciated. Thanks.

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CSK
New member. First post. Original 944 owner and now have acquired from a friend a 2001 2.7 Boxster with 115k miles and many problems. This car passed emissions last year but dealer told former owner the cats were failing. Have tracked down and remedied most problems. Last action was to replace all oxygen sensors based on fault codes(P0150 & P1130 and age), clear all remaining codes due to battery disconnect and attempted drive cycle. Drive cycle has not reset all readiness indicators (secondary air system remains at fail) and fault codes P0420 and P0430 have now appeared for the first time since my ownership. At present these are the only engine module codes. I am seeking wisdom from those wise in the ways of 986. First question is, in the presence of known good oxygen sensors, what component failures could produce these codes, other than converter failure? i.e. where should I look, test and certify before spending big on replacement converters? I have scanned the first 150 pages of posts looking for information and understand the issues of “jeff in VA” (Check Engine Light=> 2 new cat converters) but issues raised in his post appear to remain unresolved. Second question concerns available replacement converters if they are needed. I see ads for Porsche, DEC, USA and Davico. Is anyone experienced with these brands? Comments? Any and all input will be appreciated. Thanks.

Dealt with a P0420 code off and on for a couple of years. (The converter brick was loose -- probably due to some road debris hitting the converter -- and occasionally would get cock-eyed and not work as efficiently.)

You did the right thing. The factory diagnostic guidelines call for if the P0420/P0430 code is accompanied by any O2 sensor errors to replace the sensors indicated, clear the codes, and road test the car.

If the P0420/P0430 codes come back to replace the indicated converters.

What I ended up doing was buying a couple of exhaust manifolds -- into which of course the converter is integrated. I made sure both used manifolds/ converters were quiet when shaken and when turned this way and that nothing fell out. Then I was very careful with them to not bang them around. I had a Porsche tech swap the old converters with the used ones and the used ones proved to be just the ticket. The original noisy/bad converter of course was no longer and the error code stopped showing up. The noise -- dull deep knocking when cold and an irritating buzzing noise when hot -- was gone. And thankfully the other converter meant I didn't regret replacing the original factory converter -- which was working just fine -- with a bad used one.

However, I am kind of reluctant to recommend you consider used converters. Or replacement converters. In CA it is I understand against the CARB rules to use used converters. There are CARB approved replacement converters available. (I don't know how much they cost. The factory converters are/were a few years ago last time I got a price quote over $1000/each. I paid $450/each for the used converters.) Don't know where you are but if you are in CA or one of the states that subscribes to CA's extra strict emissions rules/regulations used converters may not be an option.

It is kind of rare for both converters to fail at the same time. This makes me wonder if there is something else going on, a common failure, that could account for both converters acting up concurrently?

You got the car from a friend. Do you know the car's history well? Was the car tracked? Tracking is hard on converters and can send them to an early grave. Or did perhaps the previous owner run leaded gasoline? Or use a fuel additive -- octane booster perhaps -- with some MMT in it?

You want to be sure the exhaust manifolds are not leaking. That the secondary air injection system appears to have a problem is a bit troubling too. If this is not working right, it can result in outside air getting into the exhaust and this can affect converter efficiency.

You may want to look into getting that secondary air injection system problem diagnosed and corrected then revisit the converters.

Thanks for your input Mark. When I resolve all this I will update this post and share my experience.

I would check the wiring on the sensors first since that was recently changed and it would cause this problem.