[f82_spooly]

Ran into a weird issue. I had a 2C32 code and the scanner stated it was bank 2 pre cat. So I changed the sensor I'm pointing to now which is supposed to be bank 2 pre cat the grey wire right?. I drove for like 3 hours then it came back again? Wtf? So I googled around and read that 2C32 is after cat according to this post? Which is it? Did I change the wrong sensor ?

In addition to the 2C32 code I also got a 2C6C code which said Bank 2 POST CAT? But I figured the O2 from the post cat doesn't really od anything and its the pre cat that controls the AFR and stuff. So could it be the post cat triggering the pre cat code? Should i change that sensor as well?

"2C32 - Lambda probe in front of catalytic converter, trimming control Typically caused by the wrong O2 sensors in the wrong downpipe or a major exhaust leak. Grey wire loom goes to the back pipe, black wire loom goes to the front pipe."

Also I have stock downpipes.

[Velocity26]

The rear sensors are only intended to let you know that the cats are not performing.
If your cats are missing they will do nothing useful, but they can still cause codes if they are reading out of range or are missing. I was having similar problems where bank 2 was throwing every mixture control, lean, fuel trimming code known to man. I decided that I should replace them all while I was at it and all of my codes are gone and the car drives 100% like new. I was getting surging and constant codes to where I could never drive without the SES light on.

I got the pre-cat Bosch O2's for about ~$75 each and the post-cats were a little more expensive. Check Amazon and they are all there.

[mj6234]

I had those codes and were resolved by post cat sensor replacement.

Here is my experience with the trimming control code.

The code references the primary O2, but REALLY involves both O2s.

The code seems to trigger when some kind of 'test' integrated in the DME runs. I had a 2C7C (bank 2 post cat signal code). I noticed that when it was triggered, when cruising on the highway the DME would execute some kind of routine to make sure changes seen by the primary O2 were also seen by the secondary O2.

Here's what I saw. The primary O2 A/F would slowly wander away from 14.7:1 and trend up lean. I saw it go up to ~17:1. Then it would go to 12:1. Then back to 14.7:1. I am assuming the DME changed fueling at cruise and then observed if the secondary O2 readings also changed. If it doesn't complete the 'test' successfully, you get the 'system check' (2C6C for bank 2) codes.

Before I replaced the secondary O2 sensor, sometimes the AFR on bank 2 would get stuck at 20:1. It just would keep getting leaner during the 'test' until it pegged out at 20:1. Car still ran OK, but had to be running in open loop.

Anyway, the signal code (2C7C), system check code (2 of them, one on the primary O2 and 1 on the secondary O2), and the trimming code were resolved by changing the secondary O2 (in my case).

[f82_spooly]

Thanks for the info. Is there a DIY to replace the Bank 2 post cat sensor? I already replaced the pre cat bank 2 and 2C6C refers to Post cat bank 2. So I'm guessing the post cat bank 2 sensor is also a grey wire like the pre cat bank 2 sensor?

Originally Posted by mj6234

I had those codes and were resolved by post cat sensor replacement.

Here is my experience with the trimming control code.

The code references the primary O2, but REALLY involves both O2s.

The code seems to trigger when some kind of 'test' integrated in the DME runs. I had a 2C7C (bank 2 post cat signal code). I noticed that when it was triggered, when cruising on the highway the DME would execute some kind of routine to make sure changes seen by the primary O2 were also seen by the secondary O2.

Here's what I saw. The primary O2 A/F would slowly wander away from 14.7:1 and trend up lean. I saw it go up to ~17:1. Then it would go to 12:1. Then back to 14.7:1. I am assuming the DME changed fueling at cruise and then observed if the secondary O2 readings also changed. If it doesn't complete the 'test' successfully, you get the 'system check' (2C6C for bank 2) codes.

Before I replaced the secondary O2 sensor, sometimes the AFR on bank 2 would get stuck at 20:1. It just would keep getting leaner during the 'test' until it pegged out at 20:1. Car still ran OK, but had to be running in open loop.

Anyway, the signal code (2C7C), system check code (2 of them, one on the primary O2 and 1 on the secondary O2), and the trimming code were resolved by changing the secondary O2 (in my case).

[MJ80.]

Hey bud i was having essentially the same issue getting those pre cat codes. I replaced both my pre cats and the issue improved dramatically, however now throws a post o2 code on rare occasion.

Somtimes a faulty post cat sensor can actually throw a pre cat error because it thinks that o2 isnt functioning, when it is the faulty one. Replace your posts now and you should ve sweet, thats what im doing.

[Velocity26]

The post-cat O2 sensors have a slightly different connector from one another and the wires are only about 15" long. There is one for each bank and they plug into the wiring harness right beside the bottom pan of the transmission.

It would make the process a lot easier if BMW had made the pre-cat sensors plug in near where they are located, instead of having nearly a 5' cord and requiring you to remove the engine cover and route the wiring through their difficult to access wiring looms to get to the top of the valve cover.

For those curious, the cost of these sensors varies greatly. The actual sensor itself is similar (if not identical) but the length and color of the wiring is different, to identify which location it was designed to fit. The only difference in the pre-cat O2 sensors is the length of the wiring and color of the shielding ... one wiring harness is about 6" longer than they other. The long one is a universal sensor that is used by many models and is available very cheap (~$75) while others cost significantly more because the length of the wires (and color) are specific to the N54 engine. You can use the cheaper (long) O2 sensor on both of the pre-cat sensors by simply marking the connector as to which is bank 1 and bank 2 and securing the extra wiring. The rears also vary in price, but you have to swap over the connector to use a universal connector on both banks.

[gingerbreadman]

Originally Posted by MJ80.

Hey bud i was having essentially the same issue getting those pre cat codes. I replaced both my pre cats and the issue improved dramatically, however now throws a post o2 code on rare occasion.

Somtimes a faulty post cat sensor can actually throw a pre cat error because it thinks that o2 isnt functioning, when it is the faulty one. Replace your posts now and you should ve sweet, thats what im doing.

any updates on this? I was getting 2cf7f which is lambda probe after post cat bank 2 i believe. ordered new ones from ECS and a month later, i'm still getting the same thing. Please help

[f82_spooly]

Originally Posted by gingerbreadman

any updates on this? I was getting 2cf7f which is lambda probe after post cat bank 2 i believe. ordered new ones from ECS and a month later, i'm still getting the same thing. Please help

I ordered the oxygen sensor for the post cat bank 2 -->

https://www.eeuroparts.com/Parts/196...-6-0258010414/

this is the correct one right? ^

Should be getting it this thursday or so and then I'll install and report back to you guys

[f82_spooly]

2cf7 is related to the throttle body i think?

[gingerbreadman]

Originally Posted by e92life

2cf7 is related to the throttle body i think?

Thank you. that was the wrong code. I have P2C7B.