Turbocharger/Supercharger "A" Underboost Condition
Boost pressure under load is below the commanded value. Very common on turbodiesel and direct-injection turbo gasoline engines as the turbo system ages — typically a leaking boost pipe, a sticky variable-geometry vane assembly, or a wastegate that no longer holds.
Affected components
- Turbocharger
- Intercooler
- Intercooler pipe
- Wastegate actuator
- Vgt actuator
Common causes
- High likelihood: Leak in intercooler pipe or hose
- High likelihood: VGT vanes stuck (diesel, soot buildup)
- Medium likelihood: Wastegate stuck open or weak spring
- Low likelihood: Turbo bearing worn (preceded by oil consumption / smoke)
Possible symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
- Reduced-power or limp mode may occur
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.