Help with codes 2C31 and 2C2C

[SlowX6M]

2012 5.0, just started getting these two codes.
2C31 - Lambda probe in front of catalyst, trim control
2C2C - Lambda probe before catalyst 2, system check

These seem to be O2 sensor codes, before catalytic converter, but I don't understand if they are for different banks, or the same bank? If two different banks, would be strange for both of them to fail at the same time.

[jbash87]

Some quick googling says 31 is a generic lamda code issue, while 2C refers to bank 2. Bank 1 would be 2B. I would think you'd get a 31 with either bank.

[SlowX6M]

Originally Posted by jbash87

Some quick googling says 31 is a generic lamda code issue, while 2C refers to bank 2. Bank 1 would be 2B. I would think you'd get a 31 with either bank.

That's what i figure as well. 2C2C says lambda probe before catalyst 2, signal or value above threshold. I read that it might not be the O2 sensor itself, but rather something else that is causing fuel trim out of range. I am thinking maybe I swap the left/right O2 sensors, and see if the error persists, or pops on the other side - this will tell me whether it's the O2 sensor failing, or something else causing the issue.

[SlowX6M]

Swapped O2 sensors, started the car and let it idle, and it triggered an additional code 2C27. I am hoping that its just the failing sensor, and when I switched them bank to bank, now it triggered the error on bank 1, but the error from bank 2 is in the memory. I erased the codes, will drive the car around tomorrow and see what it does.

[SlowX6M]

On the N63, the drivers side is bank 2 and passenger is bank 1? Getting conflicting answers during google search.

[rovertech]

yes, BMW vee engines do have #1 cylinder on right side of vehicle. for the record yes it makes it confusing when most of other vee engines mark cylinder 1 on vehicle's left.

these is when sitting behind the steering wheel and not standing in front of engine with open hood.

[SlowX6M]

For all the complexity of the N63, replacing it's O2 sensors is probably the easiest vs any other engine, they are right on top and not exposed to any elements, so no rust.

[SlowX6M]

Well, unfortunately the two original codes came back, 2C31 and 2C2C. At least I can conclude its not a bad sensor, since I swapped them from bank to bank and bank 2 still triggers an out of range lambda condition.

I ran a short log of sensor data with Bimmerlink, everything seems even between the two banks, but bank 2 lambda values are lower across the board. Off throttle bank 1 lambda lingers around .95 and bank 2 lambda lingers around .85 - not sure if that means leaner or richer condition.

I've just replaced all the spark plugs and coils, as well as the CCV tubes. I double checked all my work, all connections are solid, no leaks. No misfires. Not sure what the next step should be. Injectors would probably cause a misfire. Tiny vacuum leak somewhere perhaps?

I am thinking of swapping the MAF sensors from side to side as well, but according to bimmerlink the airflow is dead even across the two banks, so that's unlikely to provide a result.

[jbash87]

Low reading is rich (too much fuel). You could have a leaky injector? Can you monitor rail pressure between banks 1 and 2?

Forgive my ignorance, is the N63 DI with HPFPs on each bank? For all the BMWs I've owned in my life, none of them have been a V8. I'd love to change that one day though...

[SlowX6M]

Originally Posted by jbash87

Low reading is rich (too much fuel). You could have a leaky injector? Can you monitor rail pressure between banks 1 and 2?

Forgive my ignorance, is the N63 DI with HPFPs on each bank? For all the BMWs I've owned in my life, none of them have been a V8. I'd love to change that one day though...

Yes, "Hot Vee" V8, direct injected. Don't remember if I saw a fuel pump on each bank, or just one.

I think a leaky injector would result in a misfire for sure, I get no misfires, the car runs great. Just these stupid codes.

[SlowX6M]

Never mind that, one pump per bank. Just looked at the log, average fuel pressure across both banks stays even.

[SlowX6M]

Not sure how to post excel file here, so here are some screenshots from the log.

[jbash87]

Hmmm. When was the last time you checked your spark plugs or coils?

[SlowX6M]

Originally Posted by jbash87

Hmmm. When was the last time you checked your spark plugs or coils?

I just changed the spark plugs, coils, and CCV upper tubes, and coincidentally these errors started popping up right after.

I used NGK plugs from FCP Euro and Dinan coils. No misfires, so I am confident I did the install right. Used genuine BMW CCV tubes, installed them properly.

This really seems to be some kinda vacuum leak somewhere.

[jbash87]

Originally Posted by SlowX6M

I just changed the spark plugs, coils, and CCV upper tubes, and coincidentally these errors started popping up right after.

hmmm... I know it's a blow to one's ego, but if you're getting errors right after you've done some work, you've got to go back over that work and double/triple check it. It happens to the best of us.

Originally Posted by SlowX6M

I used NGK plugs from FCP Euro and Dinan coils. No misfires, so I am confident I did the install right. Used genuine BMW CCV tubes, installed them properly.

No misfires doesn't necessarily mean complete combustion. Even the best manufacturers can let a small number of bad parts through. In the industry we call this DPPM, or Defective Parts Per Million. The goal is to reduce this, but that also means some bad parts will eventually slip through.

Originally Posted by SlowX6M

This really seems to be some kinda vacuum leak somewhere.

I don't disagree.


All this to say, I'd double check that work. Look at the spark plugs and see if you find any anomalies. I'm not a good spark plug reader by any means, but there are plenty of pictures online which detail how certain conditions will affect the appearance of a plug.

At that point you should be able to narrow in where the issue is. I could certainly be a leak in the manifold.

When does this occur? Is it right away, only when cold, only when warm, etc?

[SlowX6M]

Originally Posted by jbash87

hmmm... I know it's a blow to one's ego, but if you're getting errors right after you've done some work, you've got to go back over that work and double/triple check it. It happens to the best of us.



No misfires doesn't necessarily mean complete combustion. Even the best manufacturers can let a small number of bad parts through. In the industry we call this DPPM, or Defective Parts Per Million. The goal is to reduce this, but that also means some bad parts will eventually slip through.



I don't disagree.


All this to say, I'd double check that work. Look at the spark plugs and see if you find any anomalies. I'm not a good spark plug reader by any means, but there are plenty of pictures online which detail how certain conditions will affect the appearance of a plug.

At that point you should be able to narrow in where the issue is. I could certainly be a leak in the manifold.

When does this occur? Is it right away, only when cold, only when warm, etc?

It's very difficult to tell. I erase the error and it comes back after driving - sometimes almost right away, sometimes after a few days, which tells me that it is a somewhat intermittent issue.

I went in there and double check that all my oils and CCV tubes are tight, and they are. I don't imagine a spark plug being bad, they generally either fire or don't fire, and its more or less the same for coils, a faulty coil would cause spark not to fire and cause a major misfire.

I could technically get one extra plug and one extra coil and keep swapping cylinder by cylinder, and i see if anything changes, but I doubt its the plugs or coils. The engine runs great under all conditions - idle, moderate throttle, and WOT.

I only changed the upper CCV tubes, so maybe the lower tube on bank 2 has a slight leak. Its almost impossible to reach from the top, so I can't DIY it.

I'll see if my mechanic can do a smoke test to see if there is a vacuum leak somewhere.

[Bengineer330]

You can absolutely diy the lower CCV hoses. Passenger side is easiest. Drivers side to make it easier I would suggest finding someone with gorilla strength midget hands. Lol. But in all seriousness loosen the coolant reservoir and you can shove your hand down there and get it.

I also had the same exact experience. Replaced everything: plugs, coils, CCV hoses, pre and post O2 sensors. Still had the fault. As terrible as it sounds mine eventually went away after about 500miles after replacing the O2 sensors.

[SlowX6M]

Originally Posted by Bengineer330

You can absolutely diy the lower CCV hoses. Passenger side is easiest. Drivers side to make it easier I would suggest finding someone with gorilla strength midget hands. Lol. But in all seriousness loosen the coolant reservoir and you can shove your hand down there and get it.

I also had the same exact experience. Replaced everything: plugs, coils, CCV hoses, pre and post O2 sensors. Still had the fault. As terrible as it sounds mine eventually went away after about 500miles after replacing the O2 sensors.

Good information, thank you so much! I have pretty damn strong hands, but they are also gorilla sized, so when I looked into that space where the hose is routed to, I said no way, lol. It looks like it would be easier to from underneath the car?

Right now my car has 108k and this time I just did the two upper hoses. At 73k I had my mechanic replace all four hoses, but when i was doing spark plugs and coils I noticed some oil seepage on the upper hoses, so I replaced them. They are made out of such brittle plastic, my washing machine discharge pipe if 10x more durable. The dealer had replaced all four of them back in 2015 with just 17k miles on the car when they were doing the injectors recall, and then they replaced just one of the upper hoses at 59k when they were doing the valve seals recall.

I guess I'll order the two lower hoses and try to tackle them, if that doesn't work I'll just have my mechanic do it. And might as well get two new precat O2 sensors. Did you go with genuine sensors, or Bosch OE sensors?

Also, did the error go away after 500 miles by itself, or did you have to keep erasing it until it stopped triggering? Did you reset fuel trim adaptations?

[jbash87]

Originally Posted by Bengineer330

You can absolutely diy the lower CCV hoses. Passenger side is easiest. Drivers side to make it easier I would suggest finding someone with gorilla strength midget hands. Lol. But in all seriousness loosen the coolant reservoir and you can shove your hand down there and get it.

I also had the same exact experience. Replaced everything: plugs, coils, CCV hoses, pre and post O2 sensors. Still had the fault. As terrible as it sounds mine eventually went away after about 500miles after replacing the O2 sensors.

Glad someone with some actual experience on this issue can pipe in. I'm just shooting from the hip generally towards where SlowX6M is pointing

[Bengineer330]

I just bought the Bosch O2 sensors. Like you mentioned the car drove fine with these codes in all conditions. I probably drove over a thousand miles before getting to the sensors. Then once I replaced them, cleared the code, it came back. It wasn’t until after admitting defeat that one morning the check engine light just wasn’t on and the code never came back.

As for doing the CCV tubes, I’ve done them a few times now so I have the process down. First time can be frustrating, if you do tackle it. Start on the passenger side to understand how they clip onto the intake manifold. If you’re keeping the car for awhile you can go the extra mile and wrap them in a silicone tape as well for added protection.

[SlowX6M]

Originally Posted by Bengineer330

I just bought the Bosch O2 sensors. Like you mentioned the car drove fine with these codes in all conditions. I probably drove over a thousand miles before getting to the sensors. Then once I replaced them, cleared the code, it came back. It wasn’t until after admitting defeat that one morning the check engine light just wasn’t on and the code never came back.

As for doing the CCV tubes, I’ve done them a few times now so I have the process down. First time can be frustrating, if you do tackle it. Start on the passenger side to understand how they clip onto the intake manifold. If you’re keeping the car for awhile you can go the extra mile and wrap them in a silicone tape as well for added protection.

I think these CCV tubes are basically a maintenance item that should just be done with every spark plug change, due to their brittle nature and high potential for vacuum leak. I've ordered two pre-cat O2 sensors and both lower CCV hoses, will try and tackle the job once the parts arrive. Thank you for the help, and I will keep this thread updated on how things work out.

[SlowX6M]

So the weather has been great in NY, and I haven't touched my car since Saturday, have been riding one of my motorcycles, and my wife has been driving my car instead of hers because it's more suitable in the winter.

Meanwhile, I had ordered the lower CCV hoses and two pre-cat O2 sensors. The order arrived early this afternoon, and soon as my wife got home from her errands I went out to change out the O2 sensors. I first went to start the car to erase the code, and lo and behold, the CEL was off.

Connected to Bimmerlink, read code memory, it shows 2C21 and 2C2C but says the fault has not yet occurred. I hope that maybe after I replaced the spark plugs and upper CCV tubes, it took the ECU a while to adjust the long term trim, and now the CEL is off for good.

I still replaced both O2 sensors, just because - after 109k miles, might as well. My wife is driving my car to VA tomorrow and back next week, hoping the CEL stays off.

P.S. When I took out and swapped the old O2 sensors from side to side, I cleaned them up with sensor cleaner. When I took them out today, they were covered with black soot, just like when I first took them out. I assume this is normal and to be expected.