BMW turbo failure?

Hi all, I have a 2008 BMW 335i with 144k miles. A couple months ago I started getting error codes for low boost pressure and following some advice online I went ahead and replaced all my vacuum lines as well as the charge pipe from the FMIC to the throttle body after finding a few leaks but the problem has persisted. I know that sometimes the actuators which control the waste gates can be the culprit but after testing those they are in working order as well. In the last month or so I have also been getting a bit of a siren noise coming from the turbos between 2000 to 3000 rpm especially when the car has just been started. So my question is, does it look like it’s time to bite the $1800 bullet and install new turbos or is there something I may have overlooked so far in my diagnosis? Unfortunately I think I may already know the answer to this but I figure it doesn’t hurt to ask. Thanks for your help!

Also, I haven’t yet seen any smoke coming from the exhaust indicating a major oil leak in the turbos and my oil consumption has been at normal levels

Have you posted this on BMW forums?

When the engine is cold, remove the hose from the compressor side of the turbo and and wiggle the vane to check for excessive play in the turbo shaft.

There will be a very slight amount of play to compensate for when the shaft and bearings expand from the heat. But if the shaft wiggles quite a bit, the turbo bearings are worn.

If you find this to be the case, check and see if you can find a turbo rebuild kit. Because turbo’s aren’t that difficult to rebuild.

But if you find the vane is hitting the turbo housing, the turbo has to be replaced.


Thanks for the tip tester, and texases I have checked on a BMW forum but I felt everyone was pushing for me to upgrade my turbos for the sake of higher performance regardless

I understand. Fanboys. I wouldn’t do any changes, your 335i is already tuned for high output. Have you looked for local BMW shops with good reputations?

Haven’t had a chance but that will be my next stop. And then time to see if this really can be a DIY job

I’d dig in there a little bit and make sure the turbochargers have actually failed. If the impeller shafts are not loose and they rotate freely they should be good.

I’ve changed a number of turbochargers and the biggest problem is usually access and/or wrestling heat frozen nuts and bolts.

If you have been diligently using FULL Synthetic motor oil your Turbos should be fine. There are many many places to look before buying new turbos…they honestly dont just fail in the manner you describe. I agree with Tester (As Usual…He is almost Always correct and its getting boring lol) Check the play in the Turbo shaft.

I would also look for leaks anywhere from the turbo to the throttle body. This BMW should have an intercooler…those can crack and leak boost pressure. Even a simple little relay could cause the Turbos to dump all their boost on purpose. If the car thinks it is already running at boost or cannot measure manifold pressure it will default to no boost as a safety measure. The MAP sensor plays this role for the engine management computer.

I would also look on the BMW specific forums on a flowchart to check when not getting any boost…there is a VERY Specific set of things that need to occur for you to get boosted…This is honestly your very first step.

I would leave the thought of your Turbos as the culprit for Very last…they are actually quite reliable pieces of kit.

Go online anywhere and look up the troubleshooting steps for this vehicle when you are not making boost…you will be surprised at all the things you have to check…many of them will be vacume hoses and relays believe it or not…a few sensors as well but the troubleshooting steps will quickly get you on the path to Boost Baby. Let us know what you find and know that your Turbos are the least likely suspect in the list.


This can be a DIY job however you are lacking the diagnosis. I would pay for that at least as replacing the turbo’s may actually be a loose line or broken sensor. Without the the manual/diagnosis tree you are shooting in the dark. Unfortuantely a new turbo(s) are $1800 and may do nothing for you.