Diagnostic Trouble Code

P0299

Turbocharger / Supercharger Underboost Condition

What the code means

The ECU isn't seeing the boost pressure it expects.

P0299 indicates that the measured boost pressure is lower than the engine control module expects under the conditions in which the fault was detected.

Importantly, this code does not automatically mean the turbocharger itself has failed. The cause can be elsewhere in the air, vacuum, control or exhaust system.

Possible causes

What could cause P0299?

Boost or charge-air leak

Split or loose intercooler hose

Turbocharger control fault

Vacuum supply problem

Wastegate or actuator problem

Variable-vane mechanism fault

Airflow or pressure sensor issue

Exhaust restriction or related engine fault

Diagnostic approach

What should you check?

1. Read the full fault memory. Check for other codes that may explain why boost control is affected.
2. Inspect the intake and boost system. Look for disconnected, damaged or leaking pipework and intercooler connections.
3. Compare requested and actual boost. Use live data to understand when and how the pressure fails to meet the ECU's target.
4. Check the control system. Depending on the vehicle, inspect vacuum supply, electronic actuators, wastegate operation or variable-vane control.
5. Test before replacing parts. Prove the cause of the underboost condition rather than assuming the turbocharger is faulty.

See a related fault diagnosis in practice

This Speed Tweaks video covers a related real-world diagnostic job and provides useful additional workshop context.

This is related workshop content rather than a dedicated P0299 guide. A dedicated diagnostic video can be added here in the future.

Watch on YouTube →

A useful thing to remember

A fault code describes something the control system has detected. It does not necessarily identify the component that caused it.