Turbo/Super Charger Bypass Valve - Mechanical

Possible causes

• CommonSplit, perished or disconnected boost hose or intercooler pipe
• CommonVariable-vane mechanism sticking with soot, on a diesel used for short journeys
• CommonWastegate or bypass valve seized, or its actuator failed
• CommonBlocked air filter or restricted intake
• PossibleBlocked diesel particulate filter raising back pressure
• PossibleWorn or failing turbocharger

What you might notice

• Noticeably flat performance
• Limp mode
• Whistling or hissing under load
• Black smoke on a diesel
• Worse fuel economy
• Check engine light on

What to check, in order

1. Check every boost hose and intercooler pipe for splits and loose clamps. This is the single most common cause, it is visible, and it costs almost nothing to fix.
2. Check the air filter - a neglected filter restricts intake air and produces these codes.
3. On a diesel used mainly for short trips, suspect the variable-vane mechanism sticking with soot. A long run at higher revs sometimes frees it and is worth trying before spending.
4. Check the wastegate or bypass valve moves freely.
5. Watch commanded against actual boost on the live data screen through an acceleration.
6. Suspect the turbo itself last. It is by far the most expensive item here and by far the least likely cause.