phild328

I need help with P0421 and P0431 codes. Warm up Catalyst Efficiency Below Threshold Bank 1 (P0421) and Bank 2 (P0431). So I bought a 06 Boxster S a little while ago. I still haven't gotten to drive it legally since it won't pass emissions.
When I got the car, it had additional code for secondary air. The secondary air pump was dead, frozen up (or maybe melted up). So I bought a used pump and installed it. Took care of the secondary air codes, but I still get the P0421 and P0431. So I replace the post-cat O2 sensors. Same thing, no change. So I take the cats off and clean then. Same thing, no change. Driver side looks good, no clogging before or after cleaning. Passenger side wasn't clogged, but cleaning caused some of the cell to disintegrate on the outlet side. I happened to get the secondary air check valve with the used one, so I swapped that as well, no change. I tried to attenuate the O2 signal with an RC filter, that didn't work. I didn't change the primary o2 sensors, because they look like they are fairly new and have already been changed. The car has 44K miles btw.
It seems that the 06 3.2 is the only car and only year with these headers. They are equal length headers with large tubing and the cat is 200 cell. I would really prefer not to buy "cheap" aftermarket un-equal length headers to replace these nice free flowing ones. See pic below.
So some questions:
1. Someone mentioned that Porsche factory had an ECU update to relax the cat eff monitoring for the 06. Can anyone confirm this? My Porsche dealer can't.
2. What does it mean by "Warm Up" eff? My check engine light comes on after I have been driving for quite some time, so it seems weird. Is the warm up of the cat or the engine? Or neither and it just calls it that?
3. When does the secondary air pump run? In the 986, the air pump check valve had a vacuum connection, the 987 doesn't. My guess is the 986 would just run independent of rpm and throttle and that the valve would close under high exhaust pressure to protect the pump. And in the 987, the computer controls the pump and just turns it on and off as needed?
4. I have read people say that the MAF sensor could be involved. How? Why?
5. I have read people say exhaust leaks could be an issue. I find this really hard to believe.

Thanks,

Soul Performance

I should be able to help you answer some of these questions. I also believe I have a set of those exact factory headers here, couldn't find any part numbers on them so this answer some of my own questions haha. Give me a ring anytime, happy to chat about this and point you in the right direction.

Best regards,
John Gaydos

dovecom

I have the same code issues on a 2.9 engine. MAF is what my tech suggested. The air pump runs only at start up. You can hear and feel it. It pumps extra air into the exhaust to burn any fuel unused by the cold engine.

dovecom

I have the same code issues on a 2.9 engine. MAF is what my tech suggested. Still waiting for the engine to test itself. The air pump runs only at start up. You can hear and feel it. It pumps extra air into the exhaust to burn any fuel unused by the cold engine.

Rip Van Winkle

Phild328, Please keep us updated on your status and solution. I also have an '06 BS with a P0421 code and the original exhaust. I have replaced all of my plugs and coils, air filter and the AOS. I have been adding Techron to my gas and resetting the CEL but the code comes right back The car runs great otherwise. And since I live in rural America, I can legally drive my car with only modest angst over destroying the environment. I am just tired of seeing those blasted lighst on the dash. I just ordered a set of those special bits and I'll try to see if I can clean the MAF this weekend. I really don't want to replace the cats if I don't have to.

dovecom

FWIW, I have an aftermarket header, stock muffler and an ECU tune designed to avoid CEL from the missing cats. It worked fine and I’ve no reason to think this is exhaust related. My downstream O2 sensors do work. I don’t know about the upstreams.
I’ve not found any info on testing or replacing the secondary air pump on these cars. It’s vastly different from the 986.

Oddly, my fuel tank ventilation is failing the readiness tests. Any ideas? Yes I’ve checked the cap.

How hard/expensive is the AIr Oil Separator on a 987.2? 2.9l engine?

TRINITONY

. https://www.ebay.com/itm/O2-Oxygen-S...QAAOSwtOVdCuZB

dovecom

I tried the mini-cats, a step beyond that suggestion. One side worked, the other didn’t. Tried a second cat, no go. Some cars just don’t work with those. I had to buy an ECU tune to fix the issue.
I now have three plus the 90 and 45 deg adapters for sale if anyone wants.
Thanks for trying though. I appreciate it.

phild328

I finally got the correct torx bit to get the MAF out. It is a 5-point torx, they are sized TS20,TS25, etc. I forget which size worked now, probably TS25. So I cleaned the MAF with MAF cleaner and put it back in. I also replaced the air oil separator (to answer a previous question, these are under $50, even rockauto has them). I also replaced all my spark plugs and checked out my cylinders with a borescope. My #2 cylinder is has a decent amount of scoring. It was the first one I looked at and I was all alarmed. The rest got better from there. Though some have some weird shaped marks, its not scoring the typical scoring, I don't know what it is. (anyone concerned with scoring? people are still paying $20k for these cars that are doomed. mine is 44k miles) All plugs looked good and equal. The engine doesn't smoke. Here and there it will smoke on start up, but that is normal for horizontal cylinders. I changed the air oil separator because I saw oil in the intake plenum, around the area of the resonance flaps(small puddles). I saw that because I had it off to change the air pump. By the way, I tried an aftermarket air pump and it did not work as well as a used original. It might flow as much air, but if you apply back pressure, the pressure dropped, it couldn't "push" the air as well, it leaked back through its fan. So my air pump is working, good, tested, and compared to a "new" one. So the China one is not as good as the USA one (yes one part on it not made in germany, germany or porsche must have regulations on sourcing parts made in germany)
Anyway, after much driving, my bank 1 did NOT code. Before before banks would throw CEL. BUT bank 2 did code. I actually got 7 of 8 readiness checks, which would get me through emissions, had it not coded. So now, back to the drawing board, bank 2 might still be dirty from oil from the air oil separator. Or from MAF issues. The MAF was not dirty, it was perfectly clean. I still cleaned it anyway since it is so sensitive even an invisible film could cause an issue.The weird thing is my bank 1 cat is in worse shape than bank 2. Bank 1 is disintegrating on the back side. Bank2 looks nice on the other hand.
I was all ready to buy a set of cats on ebay, there are some really nice stainless free flowing ones from the UK, $1200 for the set. But now since bank 1 was ok, I feel I should hold off. I don't necessarily think the cats are bad. I had replaced the downstream O2s, didn't make a difference, old ones looked good. Upstream I didn't replace because they look new, look good, and seem to perform correctly. I think I will buy one and put it on bank 2 and see what happens.
One more question:
Would low O2 heater voltage cause these codes?

My car is a flood victim. It has issues in the fuse panel and relays at the driver footwell. I noticed there is a separate fuse for the o2 heaters. Which might have conductivity issues. I measured heater voltage at the downstream o2 plug and it was only around 10V. That is with it unplugged. If it is on the same circuit as the other bank, maybe that was bringing it down. I didn't measure with both of them "open". Anyway, I was expecting 12-14v. I don't think there would be any converter that would reduce it to 10v, and if that is resistance with only 1 connected, then with 2, the voltage could drop further to 8 or 6V. That could definitely change the heating characteristics of the O2 sensor, and may throw this "warm-up" code???
Does anyone have a wiring diagram? I could also use a shop manual, I saw someone on here had one, if you could PM me a link, much appreciated.

phild328

I put on the aftermarket cats and still get the codes.
Can anyone send me a shop manual and/or wiring diagrams?
Would low voltage on the o2 heaters cause this? Has anyone ever measured the voltage at the o2 sensor? I would assume it should be system voltage between 12v-14v. Does it go through a relay? I don't see a relay for it. I assume the white wires are the heater wires?

dovecom

this is a helpful explanation of testing O2 sensors:

phild328

I still haven't fixed the issue. I am looking for some specifics to Porsche. But I am also interested in why it is referred to "Warm up". I think that is the key here. So MAF issues could make sense that during warm up, the main o2 sensors aren't controlling mixture, it would all be done by a guess based on MAF. So I would think if it is running rich, the cats don't have any oxygen and would not work? My MAF looks clean and I cleaned it, so I am going to put this down on the list for now.
Next would be the heaters in the o2 sensors. I found some wiring diagrams and it looks like they are driven right off the ECU. I would think a heater has pretty much current draw and you wouldn't want to mess up your ECU voltages by driving them directly. Mine measured at 8 volts, which seems low and I am going to go this route. Does anyone know how the ECU is designed, does it have a physical relay in it to turn this on and off or is it MOSFET driven? See my car is water damage car and some of the relays went bad from corrosion. So it could be highly likely.

dovecom

McLean doesn’t mean fixed. The sensor could still be bad. Watch that video and you’ll learn all about the heater wire and how to test it. I’m about to do the same thing. Considering their cost it’s worth testing the O2 sensors first.

yachtfund

I just recently resolved this problem on my 08 CS. Started out by replacing o2 sensors myself but it came back and I spent a lot of time speculating and testing what it could be like exhaust leaks or MAF or any number of other things but I took it to my shop and it was just a failing cat. I know that a bunch of early cars like 05 boxster and any 06 cars in particular came from the factory with cats that were very prone to failure. Lots of documented examples of cars with cats that were physically disintegrating before 40k miles. Also for these warm up codes to be triggered, I have heard that it takes as little as the cats operating below only 95% efficiency which is quite small parameters. I've heard of several cases where dealerships reflashed the ECU to widen those parameters but most of those cases where back when this would have still been under the emissions warranty. Theres plenty of threads on here and all the other forums of people working through this problem. Worth reading through some to see how other people fixed it and what they suggest. Personally I was ready for an upgrade and a bit more volume so I got a set of Soul Performance 200 cell catted headers. Totally worth it. Wish I didn't wait until my cat had failed to get them, they're amazing.

dovecom

great for you. Not my issue though. I have no cats. replaced the headers and use softronics to lie about the downstream O2 sensors. I'm zeroing in on the other pair of sensors. Local shop couldn't diagnose it either. The car refuses to finish a drive cycle so there's no cel, just too many not ready codes. SO I'm thinking the heater function of the O2s might be the issue. The procession moves on. I've replaced the MAF and AOS so far. That was fun.