BMW 120308: Charge Pressure Too Low (Turbo Underboost)
BMW fault code 120308 means the engine computer sees boost pressure staying below target, so it switches boost control off and puts the car into reduced power. On B38 and B48 engines the most common causes are a worn turbocharger or wastegate actuator, and boost pipe leaks.
Quick facts
- System
- Engine / Turbocharging
- Severity
- Moderate
- Can you still drive?
- Short drives only, diagnose soon
- Applies to
- BMW TwinPower turbo era: B38 (316i 318i, F20, X1, Mini), N20 (320i 328i, X3, 528i), N55, B48
Also shown by some scanners as: 12 03 08
Symptoms
- Engine malfunction or drivetrain malfunction warning on the dash
- Clear loss of power, the car feels like it has no turbo
- Higher fuel consumption than usual
- Sometimes a whistling or air-leak sound when accelerating
Common causes, most likely first
- 1
Worn turbocharger or wastegate actuator
The most common cause on B38 316i, 318i and X1 at higher mileage.
- 2
Boost pipe leak: cracked charge pipe, torn intercooler hose or loose clamp
- 3
Boost pressure sensor giving a wrong reading
- 4
Diverter valve stuck or leaking
- 5
Vacuum line or pressure converter fault on wastegate control (N20 and N55 era)
Related parts and used prices
| Part | Used price range |
|---|---|
| Turbocharger 7633795 (B38, used, tested) | RM2,000 |
Prices shown are reference prices at the time of writing. Used part prices change with stock and condition; WhatsApp us for today's price.
In stock now at M.S. Motor
Not sure what is wrong? Book an inspection.
WhatsApp us your fault code and car model to book a time. We scan the car, confirm the actual fault, and quote the used part and labour before any work starts. All parts tested, with warranty.
Frequently asked questions
Can I still drive with fault code 120308?
Short town drives in reduced power mode are usually tolerable, but avoid highway speeds, heavy loads and long trips, and get the car scanned soon. If power drops suddenly or the engine shakes, stop and have the car checked before driving on.
Is 120308 always the turbocharger?
No. The code points at the boost system, not one part. Turbo and actuator wear are the most common on B38, but a torn hose or loose clamp causes the same code at a much lower cost, so proper diagnosis comes first.
How much does it cost to fix in Malaysia?
Our tested used original turbocharger for this engine is around RM2,000 plus labour. If the diagnosis finds only a leaking pipe or loose clamp, the repair costs far less than a turbo. Prices move with stock and condition, so WhatsApp us your code and car model for today's price.
Which cars does this code apply to?
Mainly the B38 three-cylinder era: F30 316i, F20 116i 118i, X1 and Mini with B38 engines. B48 320i and 330i show similar underboost codes with the same diagnosis path.
