2012 F30 Boost Pressure Control Error code 120308

[astrojase]

Hello out there,

I've read a decent amount about this error and found it can be anything from a pinched hose to needing a new turbo. I have an idea of what I think the issue is, but I want to get a consensus on what others think it is, here are teh specifics of of my car, when the error occurs and changes before it occurred.

About the Car
- 2012 BMW 328i F30, N20, ~110k miles
- added a cold air intake at ~60k miles
- car has pneumatic waste gate
- recently changed (before the first error occurrence) from 0w40 to 5w30 oil (I only include this because I know oil is involved with the turbo and wastegate

About the error code 120308
- It ONLY occurs at highway speeds, and never has happened while accelerating to highway speeds (total time of occurrences is about 10-12 now over the past 2 months)
- It sometimes happens at a constant acceleration on the highway
- twice now an additional error has appeared "Synchronization failed, CC was not synchronized when debug lock was released" error code CD0487
- doesn't happen when the oil is cold, only when its at operation temperature

Let me know what your thoughts are, outside of a new turbo ill probably be doing the repairs myself
Thanks!

[dworthy]

Welcome to the Forum!

Have you checked the charge pipe for oil? There is a pressure sensor near the throttle body that could be getting coated with oil and giving a false reading to the DME.

Also I am going to assume you are using a dry filter for the CAI? This is important as an oiled filter can foul a MAF out.

I would see about checking the vacuum lines from the vacuum pump to the turbo, plus double checking all the connections from the MAF to the intercooler, then to the throttle body. You want to make sure that charge pipe is fully operational and sealed.

[astrojase]

Thanks for responding dworthy,

Ill check the charge pipe for oil this weekend, and detach/retighten everything to make sure all the intake pipes are seated well. While I'm there Ill double check the vacuum lines. I am using a dry filter, when the error first occurred I even went though with compressed air and cleaned out the filter best I could. Thanks for the suggestion! Ill touch be back with the results.

Jason

[deanso]

Thanks for responding dworthy,

Ill check the charge pipe for oil this weekend, and detach/retighten everything to make sure all the intake pipes are seated well. While I'm there Ill double check the vacuum lines. I am using a dry filter, when the error first occurred I even went though with compressed air and cleaned out the filter best I could. Thanks for the suggestion! Ill touch be back with the results.

Jason

I have the same car and the same faultcode as well. Did you find what caused you're issue, looking for what to check first. Any info would be appreciated.

[2012bimmer]

[I just bought a used 2012 328i (as is) no warranty with 97.7k miles and on the way home I get drivetrain malfunction as soon as I hit 60mph. I took it to bmw dealer next morning then got diagnosed with the 120308 code. Have you solved your issue completely I’m shitting my pants on what this could be

- - - Updated - - -

I forgot to mention I bought it from a Kia dealer 🤦🏻*♂️

[dworthy]

Check your charge pipe, for they are made out of plastic. With plastic after 10 years of sitting in a hot engine bay, it will become brittle and break.

[Han79]

Hello,

Did anybody found out what this problem was?

I got the exact same problem after vacuumpump replacement and its driving me nuts. This reason for changing was because there was oil leaking in the vacuumsystem throught the pump. Cleaned everything and also replaced the boost solenoid. Can't find any leaks.. Checked chargepipe too, cleaned MAP sensors because they were a little oily, problem still exists.

Hope someone knows where to look next...

[Volkom]

Same problem, 120308...
Replaced diverter valve but boost tops off at 10 psi then never returns as high for the rest of the drive. Waiting on a pressure converter and about to do a pressure test and smoke test....