[Shredderphil85]

Hey There,

I am new to this forum and reaching out to the community on a 29E1 "Mixture Control 2" fault that I have been fighting on my 2008 328i Wagon for months now. I have tried almost everything I can possibly think of to identify and fix this fault with no luck. Looking at STFT's, the bank 2 value is slightly negative at idle and then immediately goes positive on throttle and will spike as high as 20%+ at times. The weird thing is that the fault comes and goes and will sometimes go away for weeks before returning. Below is what I have done so far:

Open to any and all suggestions at this point.

-Smoke leak tested twice and there are no vacuum leaks.
-Both upstream O2 sensors replaced
-MAF sensor replaced
-MAP sensor replaced
-Fuel pump and FPR replaced
-Swapped injectors from bank 1 to bank 2 and fault stayed on bank 2.
-Swapped Vanos solenoid positions in case one was bad. No change
-Evap purge valve replaced
-Related adaptations reset

[NZE90]

I've had a similar issue before. The PCV diaphram had a small split in it. Wouldn't show up with a smoke test as the split closed up when the engine was not running.

[Shredderphil85]

Thanks for the reply. I changed out the valve cover about 15,000 miles ago so I’d say it’s unlikely to be the PCV, but I’ll check it out just in case.

[gbalthrop]

Originally Posted by Shredderphil85

... 29E1 "Mixture Control 2" fault... 2008 328i Wagon... Looking at STFT's, the bank 2 value is slightly negative at idle and then immediately goes positive on throttle and will spike as high as 20%+ at times. The weird thing is that the fault comes and goes and will sometimes go away for weeks before returning...

An intermittent fault is more likely to be an electrical issue (wiring or connector) than a mechanical/component fault. I would begin by carefully examining the connector & wiring to Bank2 Lambda Sensor (Pre-Cat).

Questions:

1) Are engine performance, or fuel mileage, affected when the fault occurs? I would assume WOT performance is NOT affected? Lambda control (closed loop) is basically fine tuning the fuel mixture, and a signal wire issue in Bank2 O2 Sensor will cause fault w/o any actual mechanical issue being present.

2) Make/Model of Scan Tool or Diagnostic Software (INPA/ISTA) available?

3) According to Bentley, 29E1 can mean EITHER too Lean or too Rich. What P-code is read, P0174 or P0175?

4) What Freeze Frame Data, or Fault Details, are read?

5) What other DME Fault Codes are present?

6) Has engine ever run rough or stalled when SES light comes on or fault is present?

With answers to those questions, we can suggest Next Steps.
George

[Shredderphil85]

Checked out the O2 sensor plugs and no obvious red flags, but not to say that couldn't be it...

1. Engine performance seems ok, but possibly sluggish accelerating from low RPM's sometimes. TBH haven't calculated mpg's. Hard to tell since I've been dealing with the issue for a while now and can't remember what feels normal or not lol. WOT seems fine.

2. Using a Carly bluetooth scanner. Do not have ISTA/INPA

3. No P codes have ever been thrown(probably below OBD2 threshold). Always just the BMW 29E1. Looking at fuel trim live data, I can say with near certainty that bank 2 is lean.

4. Don't have any freeze frame data saved, but looking at it previously when a code is thrown, the faults have occurred at both low RPM and mid rpm 2500-2600 while highway driving.

5. A few times over the last 5 or so months 29F4 and 29F5 catalytic converter conversion codes for both banks have tripped a few times, but end up clearing themselves like the other code.

6. One time only recently, I had some misfires when hard accelerating from a stop. Weird thing is, the CEL was on, the car misfired and then corrected itself and the CEL turned itself off immediately afterwards.