P0299: Turbocharger underboost condition

What the code tells you on its own

• System. Powertrain. Engine, fuel, air, ignition, emissions and transmission. The overwhelming majority of what workshops bring to the AI.
• Functional group. Turbo and boost control
• Subsystem. Fuel and air metering
• Failure type byte, when the tool sends one. 00 (No sub-type information). Scan tools report the same fault as P0299 and as P0299xx, where xx is a sub-type. They are one fault, and whether the sub-type appears depends on the tool and the protocol rather than on the car.

What we see when P0299 turns up

Measured across the diagnostics run through Wrenchlane by independent workshops, not taken from a reference table. Sightings span February 2026 to August 2026.

• 55 diagnostics carried this code.
• 22 separate workshops met it, so this is not one shop seeing the same fault repeatedly.
• 22% of the time it arrived with no symptom description at all, meaning the technician had nothing but the code to work from.
• Most often on Volvo, which is where we have seen it most rather than a claim about the fleet at large.

What P0299 usually turns up with

The multiplier is how much more often the two appear together than chance would predict, so a high number means the pair is telling you something a single code is not. Codes rarely arrive alone, and reading the set is usually faster than chasing the first one on the list.

• P0049, Turbocharger turbine overspeed. Seen together 3 times, 27.8x more often than chance.
• P00BD, Mass air flow sensor A circuit range/performance, air flow too high. Seen together 3 times, 20.9x more often than chance.
• P2262, Turbocharger boost pressure not detected, mechanical. Seen together 3 times, 20.9x more often than chance.
• P0675, Cylinder 5 glow plug circuit. Seen together 3 times, 13.9x more often than chance.
• P2452, Diesel particulate filter pressure sensor A circuit. Seen together 3 times, 13.9x more often than chance.
• P2009, Intake manifold runner control circuit low, bank 1. Seen together 3 times, 9.3x more often than chance.

What this page does not tell you

A code names a symptom the car noticed, not the part that failed. P0299 on one vehicle and the same code on another can have different causes, and the counts above describe what independent workshops brought to us rather than how common the fault is across all cars. Getting from the code to the cause needs the vehicle: its make, model, engine and what it is actually doing.

Run P0299 against the car in front of you. Enter the code and the symptoms and get ranked probable causes for that specific vehicle, with the checks in the order worth doing them. Free account, no card.

Other turbo and boost control codes

• P2563, Turbocharger boost control position sensor circuit range/performance
• P2263, Turbocharger boost system performance
• P2279, Intake air system leak
• P0234, Turbocharger overboost condition
• P00BC, Mass air flow sensor A circuit range/performance, air flow too low
• P0245, Turbocharger wastegate solenoid A low