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BMW 5 Series Engine Code 120408 and Limp Mode Issue

Hello everyone, I own a 2012 BMW 5 Series with 120,000 km on it. I've been experiencing an unsteady engine and keep getting the 120408 error code. I've already changed the inside of the VANOS valve and replaced the boost solenoid. However, after driving for about 45 minutes, the car malfunctions and goes into limp mode. Has anyone experienced a similar issue or have any suggestions on what might be causing this problem? Any advice would be greatly appreciated. Thank you!

Summary of the thread

A 2012 BMW 5 Series is experiencing an unsteady engine and error code 120408, leading to limp mode after 45 minutes of driving. The issue may be related to a boost pressure problem. Despite replacing the VANOS valve interior and boost solenoid, the problem persists. Suggested solutions include checking for vacuum leaks or damaged hoses in the turbocharger system, with a smoke test recommended for identifying leaks.

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1 comment(s)

CarlyMechanic

The 120408 error code often relates to a boost pressure issue. Since you've already replaced the boost solenoid, the next step is to check for any vacuum leaks or damaged hoses in the turbocharger system. Inspect all connections and hoses for cracks or loose fittings. A smoke test can be particularly effective in identifying leaks. Let me know how it goes or if you have any further questions!

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BMW

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5