Check engine light P0421 code

Just got this yesterday. DTC severity 2 of 3. Not sure what to make of this. Gas cap and oil cap are secure. Fuel economy was 8.1 liters per 100 km (29 miles per US gallon) No loss of power on acceleration up hills and passing. All codes were cleared at my oil and filter change approximately 530 km ago. Catalytic converter failing? Failing oxygen sensor? 2008 987 Base Cayman 2.7 l engine 280711 km Any ideas? Thanks.

You can get durametric logging to determine if your cats and o2 sensors are functioning. Is this the first time this code has reared its ugly head? At this stage in the game, the cats are my estimated guess.... Age, mileage and they are/were known to be problematic (earlier TSB's) that were replaced at one time. If it is the cats.... now is the time to upgrade headers with cats. That's the best I can offer. Sent from my SM-G960W using Tapatalk

Do you think it will be safe to drive so long as the car is behaving normally and just keep clearing the CEL code?

Nobody can answer that. The code is there because there is a fault. With the mileage you have, I would certainly at the very least get an independent Porsche shop or local guy with the durametric tool to log and see what the problem is so you can decide how to proceed. Sent from my SM-G960W using Tapatalk

P0421 means your bank 1 catalytic converter isn't performing properly during warm up. There's two oxygen sensors on each bank, one before the cat to control the mixture and one after the cat to monitor catalyst performance. Likely causes are that either your bank 1 after-cat sensor is worn out, or your cat converter itself is worn out. No guarantees, but assuming the code is correct it is probably safe to drive, the only impact should be to emissions. Oxygen sensors do wear out eventually, and if they're original 280K km is a LOT of distance. I'd try replacing the one sensor (and maybe consider replacing all four, I'd suspect they're pretty worn at this point) see if that fixes the problem.

Thank you.

You can try swapping the left and right side O2 sensors . If the error message "travels" with the sensor, then you have a bad sensor. If not, you'll at least know that the sensors are good. Sent from my SM-N910V using Tapatalk

I got the same error code today. The information on this site has me understanding the issues. I am going to swap my post cat 02 sensors. One thing nobody mentions in any of the threads though, is bank one the drivers side?

[Image-only or quote-only post; no author-written text.]

Thanks. Now that is clear! In all of the years that I had this car, I have never seen the engine from above.

Ah ha, thanks for the info. Passenger side is bank 1, of course the Germans do it backwards. Seriously though, this car's design is really great. These 02 sensors are pretty easy to swap, the coils and sparkplugs are all right there too. Never expected a mid engine car to be so easy to work on.

Follow up - swapped my downstream 02 sensors between banks, drove over 50 miles and no check engine warning has returned so far. I think I fixed it. Weird weather we have having today. I had to drive over 100 MPH just to get the snow to blow off my front trunk lid heh heh

Mainsoda I fear that you have only cleared the code and it will return. The conditions have to just wrong for the code to appear. All I have a Durametric and do not understand how that device will determine if a P0421 code is an O2 sensor or a bad cat converter. If someone has an answer I would greatly appreciate it.

You could be right, but I've gone 6 days and no code. I've driven the car over 50 miles every day. I thought I might at least see the code return or go to the other side, but I think it might have been a false reading on the overly touchy 02 sensor. If my code comes back I'll change my 02 sensors and I get the feeling that will fix it. If not then it is time to get that aftermarket exhaust . Win win scenario.

Follow up: my P0421 code came back today so same bank even after swapping my 02 sensors. It does sound like a bad cat. Damn that's expensive and I can't afford to fix it right away. Car seems to be running a bit rough too even after just changing my AOS and all spark plugs and coils. The weirdest part is I just passed my Wisconsin state emissions test 2 days ago. Any tips on finding reasonably priced oem or aftermarket exhaust ? How much damage can result in letting this bad cat go for a few months?

Are you getting good fuel economy? Does the car accelerate well? My mechanic said that this code only shows that the emissions are not as clean as the reference in the car's specs. Also, I understand that these specs are more strict and demanding of the catalytic convertor's performance. The mechanic said that if the car runs well, it should be all right to drive it.