[thatgarrett]

Hello,

Yesterday I had my first experience with the "drivetrain malfunction" half engine light on the interstate, no weird noises or recent work to the car, and I pulled out my scanner and it came up as two errors:

120308- Boost pressure control, plausibility: pressure too low
138A11- Exhaust flap actuator, mechanical: blockage or sluggishness

Reset the codes and drove home on the interstate, nothing too crazy and fairly moderate driving, tried giving it a bit of gas while keeping it in gear and trigger the code again, this time only the 120308 code (in other testing, the 138A11 code never came back and the functionality of it seems normal when testing manually)

Car is stock, no tunes, 2012 335i N55 with 8AT (PWG), only modifications are an ER charge pipe I've had over a year and axleback M2 exhaust I swapped a few months ago.

I took the car home and inspected all of the fittings (hot side pipe, IC, charge pipe and its couplings) and all the connections seemed tight and seated, but I removed everything, cleaned and wiped it down and inspected it all, then reinstalled it. Did a short pull around the neighborhood and it was fine until I put it into sport and gave it some gas trying to get some boost (all the time I was running Bimmerlink watching fuel lambda and the boost values), then it set the code again. Fast forward to today, I checked all the vacuum lines visually, manually actuated the waste gate, turned on the car and checked for vacuum from the lines (across the valve cover, the smaller ones to the pressure converter, and the one running to the waste gate actuator) and they had vacuum, I also saw the waste gate manually move like it does from closed to open on a cold start. I cleaned the MAP sensor, as I had a bit of oily crud on it (from the PCV fitting on the intake) and a bit of oil around the charge pipe to intercooler connection around (small bit of oil, some dirt and crud accumulated outside, I think it has been like that for a bit). The meth bungs were all on tight too. Reassembled and took it out, got the code to trip again pulling a bit in sport, then I reset the code and took this log, there might have been a bit extra time at the end of the pull before I hit stop but it looks like I am getting lower boost than anticipated- I haven't really logged before and this is my first turbo car (but other BMW's in the past), read a bunch of the stickied threads.

Another thing to note: back when I installed my ER CP, I had it slip off the throttle body and had a huge boost leak (obviously), it was loud, the car was super slow and sluggish- this time does not feel like that and there is no notable whistling or other sounds.

Currently my best guess is a boost leak, perhaps at the IC-CP coupling? Any other thoughts or suggestions based on this? If that is the case, I'll get a shop to do a pressurized smoke test to check for boost leaks, just wanted to make sure I wasn't throwing money and time away if the log points to something else.

https://datazap.me/u/thatgarrett/201...log=0&data=2-3

[thejeremyman9]

Assuming those parameters are what we think they are - boost and boost target - even the boost target looks low. But its a bit hard to interpret the log without RPM, TPS, etc. The code does imply a boost leak, although not definitive without the test, as other issues could cause low boost. The pressure/smoke test would probably be my next step.

[thatgarrett]

thejeremyman9 thanks for the feedback, I have a spare set of o rings I’m planning on swapping on my charge pipe as I noticed it seemed a little loose at the intercooler cold side connection, I’ll grab a better log after that with the additional parameters to help readability, but I do think the target boost seemed lower than other times I’ve taken readings in the past. I’ll update with a better log then

[thatgarrett]

Update: Called a few indies in the area and talked with them and went over symptoms and troubleshooting, they said they had seen similar codes before but had little success getting to the issue and ended up sending the person to the dealer, so I booked a diagnostic with the dealer for early this coming week, rate was actually pretty reasonable and was about the same as the indies charge plus a free loaner, so hopefully I’ll get some answers soon. Still planning on replacing the parts and doing the actual work myself once the dealer pinpoints what is going on- they seem pretty DIY friendly from my interactions with them so far

[harkes]

Very common for the wastegate vacuum solenoid to fail. I replaced mine twice (130k km now).