[HalfAnP]

Hey all,

A couple of weeks ago (and 200 miles from home) I got a drivetrain malfunction message on my 35i with a noticeable reduction in power and when I slowed down I could clearly hear the exhaust rattling, luckily I had an OBD scanner with me and I checked for codes, but nothing came up. The message goes away when I shut off the car, and may or may not return when its turned back on, but when it does come on it happens under acceleration.

120308 Boost Pressure Control, Plausibility: Pressure Too Low

I'm hoping this post can be a sort of sanity check for me, as I'm new-ish to BMWs and the last couple of weeks have been spent learning both systems and tech pubs plus familiarizing myself further with the layout of the engine and components. Having said all that, this is where I'm at so far:

• Check the exhaust flap itself - The flap moves freely and no part of it appears to be damaged. I isolated the solenoid in the trunk by removing the vacuum lines and joining them together, forcing the flap open. It still rattles, so I'm inclined to tentatively eliminate the exhaust flap as a cause.
  
  
• Vacuum leak somewhere else in the system - I say tentatively, because the hose to the exhaust flap may have a leak at the nipple, but having inspected it, the hose appears to be in good condition and it is attached securely at both ends. I've checked the hoses in the engine bay and they all appear to be in similar condition.
  
  
• Faulty Charge Pipe - This is a big one for me. Six weeks or so ago, the starter in this car failed. I replaced it, but when reassembling the charge pipe a bung broke off it basically where it goes into the pipe itself. I repaired it with aviation-grade adhesive and just this past weekend re-checked it, it's still holding strong. Again, my current issues only started happening suddenly about two weeks ago.
  
  
• Faulty Vacuum Reservoir - The other big item for me (and the one I'm dreading the most). Reading up on NewTIS, the exhaust flap is fed vacuum directly from the engine-bay reservoir, which ALSO feeds the pressure converter that drives the wastegate. If the reservoir is on the fritz, it may affect both of these systems. My current understanding is that the reservoir is an integral part of the valve cover, but I haven't been able to verify that 100%.
  

I'm on the fence about some of these options because everything checks out when the ISTA suggested tests are performed. For 120308, the system physically moves the exhaust flap and the wastegate, and I can see them both move. The final step is to use a smoke machine to check for leaks, but I don't have access to one ATM.

Anyone see this problem or one like this before? any ideas whatsoever?

Thanks in advance!

[oVeRdOsE.]

I doubt its the exhaust flap, mine is disconnected and I got a ty-wrap to hold it open. No check.


My guess is the flexible plastic line from the PCV valve to the charge pipe.

Those are cracking easly. mine was dry, very very dry.

To be sure, put a insert in it. That what I did, cheap fix. I used a old plastic pipe, open the OEM flex hose , insert the plastic hose in it, tape it. make sure that the hose is blocked to avoid throwing it in the charge pipe.


the one with the QR code in the picture :

[HalfAnP]

Hey overdose,

Thanks for getting back to me! Was the crack in that hose super obvious? Mine looks pretty solid.

[oVeRdOsE.]

Originally Posted by HalfAnP

Hey overdose,

Thanks for getting back to me! Was the crack in that hose super obvious? Mine looks pretty solid.

not for me , it was solid, but dry, ''just like pastas''. So there were a lot of small rip everywhere.

[tuta]

I got the same code. My problem was the car battery, it was showing good but low CCA, I think it was 690 out of 950. replaced and no issue last 100 miles. It stopped the rattle noise and no more 120308 error.