Turbo/Super Charger Underboost

Possible causes

• CommonSplit, perished or disconnected boost hose or intercooler pipe
• CommonVariable-vane mechanism sticking with soot, on a diesel used for short journeys
• CommonFailed wastegate solenoid or a seized actuator
• CommonBlocked air filter or a restricted intake
• PossibleBlocked diesel particulate filter raising back pressure
• PossibleWorn or failing turbocharger
• PossibleFaulty boost sensor under-reporting

What you might notice

• Noticeably flat performance
• Limp mode
• Whistling or hissing under acceleration
• 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 this code.
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 that is worth trying before spending anything.
4. Check for particulate filter codes. A blocked filter raises back pressure and the turbo cannot make boost against it.
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 of this code.