How do you fix fault code P0299?

Visual Inspection: Check all charge air hoses and intercooler for oil residue or cracks. Inspect vacuum lines to the turbo actuator. Pressure Test: Perform a boost leak test using a smoke machine or pressure adapter to find leaks that only occur under load. Measurement (Solenoid): Check resistance of the boost control valve (typically 15-35 Ohms). Monitor duty cycle via scan tool during test drive (typically 20-80%). VNT/Wastegate Check: Ensure the actuator moves freely when applying external vacuum (it should hold vacuum without leaking). MAP Sensor: Verify the sensor reads atmospheric pressure (approx. 1 bar/14.5 psi) with ignition ON and engine OFF.

Powertrain (Engine & Gearbox)Standard EOBD

P0299 - Turbocharger/Supercharger A Underboost Condition

Q: What are the symptoms of fault code P0299?

• Check Engine Light (MIL) illuminated • Significant loss of power under acceleration • Vehicle enters Limp Home mode • Hissing or whistling noises from the engine bay during boost • Increased fuel consumption and potentially black smoke (on diesel engines) • Will cause emission inspection failure

Q: What causes fault code P0299?

• Most likely: Boost leaks in the induction system (cracked intercooler, loose hoses, or faulty couplers) • Likely: Faulty Boost Control Solenoid (e.g., N75 valve or wastegate actuator) • Possible: Sticking or failed Variable Nozzle Turbine (VNT) vanes or wastegate mechanism • Possible: Faulty Boost Pressure/MAP sensor providing inaccurate readings • Rare: Mechanical turbocharger failure (damaged impeller or excessive shaft play)

Last updated:1 February 2026

Related:Turbocharger, Intercooler, Boost Control Solenoid, MAP Sensor, Wastegate Actuator

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0200

Injector Circuit Malfunction

P0201

Cylinder 1 Injector Circuit Open

P0202

Injector Circuit - Cylinder 2 - Malfunction

P0203

Injector Circuit - Cylinder 3

Technical Description

P0299 is set when the Engine Control Unit (ECU) detects that the actual boost pressure from the turbocharger or supercharger is lower than the target/commanded pressure for a predetermined duration. The system monitors this via the Manifold Absolute Pressure (MAP) or Boost Pressure sensor. A significant deviation (typically >4-7 psi) between commanded and actual boost under load conditions triggers the code. This often results in 'Limp Mode' to prevent turbo overspeed conditions caused by downstream leaks.