Home › Fault codes › P0299 / 120308 (underboost)
BMW P0299 and 120308: boost pressure too low
The turbo isn't making the boost the engine computer asked for, so it cuts power (failsafe). Usually a leak in the intake or a boost control problem, not the turbo itself.
Last updated
Codes on this page
| Code | Definition | Source |
|---|---|---|
| P0299 | Turbocharger/supercharger "A" underboost condition | Generic OBD-II |
| 120308 | Boost pressure control, plausibility: pressure too low (F-series) | SI B12 16 11 (PDF) |
| 2C57 | Boost pressure control, plausibility: pressure too low (E-series) | SI B12 16 11 (PDF) |
| 120208 | Charging pressure control plausibility: pressure too high | SI B12 17 16 (PDF) |
| 120408 | Charging pressure control: switching off | SI B12 17 16 (PDF) |
P-codes are the generic OBD-II codes any reader shows. Six-character and four-character hex codes are BMW's own, read with a BMW-capable scanner; the wording is BMW's, from the source shown.
What it means
The DME compares the boost it requested with what the boost pressure sensor reads. If it stays too low (or too high), it stores a boost code and often limits power, shown as "Drivetrain malfunction". BMW's N55 bulletin is clear that the turbochargers are usually not the cause.
Can I keep driving?
Yes, gently, in reduced power. The car is drivable in failsafe but slower; avoid hard acceleration until it's fixed. If other codes such as high-pressure fuel, crank, cam or knock sensor faults are stored, BMW says to diagnose those first.
Usual causes on BMWs
| Cause | Cars most affected | What you notice | Evidence | Repair prices (national average) |
|---|---|---|---|---|
| Boost leak: charge pipe, intercooler hoses, clamps | N54, N55, N20, B58 and others | BMW's N55 bulletin lists leaks or restrictions in the induction system, loose clamps and cracked pipes or housings, and recommends a smoke test. | SI B12 16 11 (PDF) | N55 charge pipe (intercooler to throttle) replacement Indie $578–$922 Dealer $1,287–$1,744 |
| Aftermarket intake, exhaust or tuning | All turbo engines | BMW names aftermarket air filters and housings, blow-off valves, exhausts, performance cats, piggy-back modules and tuner software. | SI B12 16 11 (PDF) | — |
| Vacuum hoses and solenoids for the wastegate | N55 and other vacuum-wastegate engines | A slightly collapsed or kinked vacuum hose can cause intermittent faults under heavy acceleration; BMW suggests a vacuum gauge and blocking the exhaust-flap vacuum line to rule it out. | SI B12 16 11 (PDF) | — |
| Electric wastegate actuator | N63R (G12) and B-series engines | Reduced power and wastegate codes; BMW replaced N63R actuators under a service action. | SI B11 04 16 (PDF) | — |
| Over-sensitive boost check (software) | F87 M2 built to 8/3/2016 | 120208 and 120408 with "Drivetrain malfunction"; fixed by reprogramming. | SI B12 17 16 (PDF) | — |
A bulletin isn't a recall and doesn't mean your car has the problem; open it for the exact models and build dates. Estimates are national averages built from BMW warranty labor time, regional shop rates and parts prices; open a repair for your ZIP. "Owners paid" is the middle half of sourced prices, shown where we have at least 3.
What to do
- Ask for a smoke test of the intake and charge pipes.
- Mention any aftermarket parts or tune.
- Don't agree to new turbos until leaks and boost control have been checked.
Warnings it can bring up
Related codes
P1290 / 123401 (wastegate) P0171 / P0174 (lean) All fault codes
Other BMW bulletins that mention it
- SI B12 23 15 Reduced Engine Power with “Charging Pressure Too High” Faults Stored F06, F10, F12, F13, F15 and others · Jul 2015
- SI B12 10 13 S63T Engine Sets "Charge Pressure Too High" Fault Above 6,000 RPM F06, F10, F12, F13, E60 and others · May 2013
- SI B01 11 25 N57T EGR cooler / aux EGR cooler ext ltd wty (elw) 25 yrs/no mileage limit F01, F02, F10, F15 · Sep 2026
- SI B18 01 17 Diesel particulate filter (dpf) cleaning E46, E60, E70, E90, E91 and others · Feb 2017
- SI B01 01 25 N47T exhaust gas recirculation cooler ext ltd wty (elw) 25 yrs/no mileage limit F30, F31, F25 · Aug 2025
- SI B12 07 15 ALPINA N63TU Overboost Faults Set at High Altitude E82, F01, F02 · Jan 2015
- SI B11 06 18 Turbo boost actuator rod loose (diesel) F10, F15, F25, F30, F31 · Jun 2018
- SI B12 14 18 Individual driving cycles for obd2 readiness codes (m57y) E70, E90 · Apr 2018
17 of the BMW bulletins we hold mention it in their text; these are the closest matches.
Sources
Bulletins are cited in the tables above. Explanations are ours; where a source is an owner report rather than BMW, it is labelled as one.