P0299 — Turbocharger/supercharger underboost

P0299 means boost did not reach the expected value under the monitored conditions. Air leaks, restrictions, turbo control and inaccurate measurement can cause the shortfall, so it is not automatically a turbocharger failure. Noise or an oil trace alone is not conclusive. Diagnose the air path and boost regulation before evaluating whether the turbo itself requires repair.

Affected system: Forced induction

Symptoms

• Weak acceleration or low power under load.
• Protection mode and an engine warning.
• Possible whistling, air leakage or smoke, depending on the actual cause.

Possible causes

• Leaking hose, clamp, seal or intercooler.
• Restricted intake/filter or excessive exhaust backpressure.
• Actuator, wastegate, variable geometry or control-circuit fault.
• Incorrect MAP/boost feedback or turbo mechanical damage confirmed by inspection.

What to check

• Inspect charge-air hoses and joints first; save codes and freeze-frame data before clearing.
• Check the filter and air path for obstructions, loose components or recent repair issues.
• Compare requested/measured boost in consistent units, distinguishing absolute from gauge pressure.
• Check engine-off MAP plausibility and leak-test the charge-air path using an approved method.
• Test actuator/control according to fitted equipment; investigate DPF/exhaust restriction when supported by data.
• Stop testing for heavy smoke, mechanical noise or abnormal oil consumption. Do not replace a turbo without addressing any cause that could damage the replacement.

Step-by-step repair guide

• P0299 and P0234 (turbo limp mode): symptoms, causes and how to fix them

Also written as: P0299-00, P029900, PO299 (some scan tools add the fault-type byte, e.g. -00).