What it means
The boost pressure on branch B exceeds the calibrated maximum. Mechanical fault — wastegate stuck closed or boost control valve jammed.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The branch B boost system must regulate pressure so the turbocharger or supercharger does not exceed its calibrated limit. This code sets when boost rises above that maximum, commonly because the branch B wastegate is stuck closed or its boost control valve is jammed.
Common causes
Most likely first.
- Wastegate stuck closed
- Boost control valve jammed
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
How to diagnose it
- Review freeze-frame data and live commanded versus actual branch B boost to confirm when pressure exceeds the target.
- Inspect the branch B charge-air path and pressure hoses for damage that could affect control readings or create abnormal boost behavior.
- Check the wastegate linkage and actuator for binding or a position that prevents the wastegate from opening.
- Inspect the branch B boost control valve and its electrical connector or control hoses for sticking, blockage or damage.
- If the mechanism moves freely, test actuator and valve response and compare boost control readings with the manufacturer's specification.
Common fixes
- Repair a binding branch B wastegate linkage if it can be serviced.
- Replace a damaged or sticking branch B boost control valve.
- Repair leaking, blocked or disconnected boost control hoses or wiring.
- Replace a failed wastegate actuator or turbo assembly if testing confirms it cannot regulate boost.
Can I keep driving?
Avoid driving under heavy load because excessive boost can cause engine damage and trigger reduced-power mode. If power surges, smoke appears or the engine runs abnormally, stop safely and have the boost fault checked.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.