P0299 fault code: Turbo/Super Charger Underboost

Last updated · OBDCode UK editorial

Can I drive with P0299? — Drive only if essential

Limit driving to essential journeys until a garage has found why boost is low. If power collapses, you hear a loud hiss, or the engine management light flashes, stop and arrange recovery.

P0299 means “Turbo/Super Charger Underboost” — a fuel and injector circuits fault in the powertrain. Drive only if essential. The engine computer has measured less boost than it asked the turbocharger or supercharger to deliver. Power may feel flat. That reading alone does not prove the turbo unit has failed.

Can I DIY?

Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage.

Caution — conditions applyDIY boundary
ToolsBasic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.

Some checks may be possible for a careful DIY driver with the right tools and a safe place to work. Stop if anything feels beyond your skill or kit.

Hot systems

Never open a hot coolant cap — pressure can scald you. Exhaust and catalytic converter get hot enough to burn and ignite debris. Stay clear of electric fans; they can run after shut-off.

P02xxFuel and injector circuits
MOT fail riskif the warning light stays on

What does P0299 mean?

P0299 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P02xx block, which covers fuel and injector circuits. The stored description is “Turbo/Super Charger Underboost”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

How to diagnose P0299 yourself

  1. Confirm P0299 and freeze-frame: Scan with an OBD-II reader while the car is stationary, outdoors. Note whether P0299 is current or pending, freeze-frame load if shown, and every other stored code. Stop if: The engine management light is flashing, the engine is overheating, or you smell strong exhaust in the cabin.
    Generic driver footwell showing a broad OBD-II socket search zone and the usual 16-pin socket shape.
    Park safely and switch off before locating the socket. Its position varies, so use the vehicle handbook and never force or dismantle trim.
  2. Look at boost and intercooler pipes: Open the bonnet on firm level ground with the engine off. From above, look for split, collapsed, or disconnected rubber boost and intercooler pipes. Do not squeeze hot pipes or reach past the cooling fan. Stop if: Pipes are too hot to be near, the cooling fan may run, or you would need to raise the car to see the rest of the pipework.

Will P0299 fail an MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. Clearing P0299 without fixing the boost fault is not a repair.

Before booking your test, check what usually fails on your car: see our MOT pass rates by make and model, built from 33.1 million DVSA tests.

What the MOT data says

No MOT certificate item corresponds to this code; MOT outcome data cannot be shown.

Related guides

Car diagnostic test cost: compare the scopeUK booking marketplaces currently publish diagnostic averages of about £52–£65. Engine management light on: steady or flashing?A steady engine management light means the computer has stored a fault. Drive with caution and get the code read. A flashing light is different — stop when it is safe. Car loses power when accelerating: safe next stepsReduced power is a symptom, not a parts diagnosis; leave fast traffic and preserve warning and code evidence.
P0200Injector Circuit/Open P0201Injector Circuit/Open - Cylinder 1 P0202Injector Circuit/Open - Cylinder 2 P0203Injector Circuit/Open - Cylinder 3 P0204Injector Circuit/Open - Cylinder 4 P0205Injector Circuit/Open - Cylinder 5 P0206Injector Circuit/Open - Cylinder 6 P0207Injector Circuit/Open - Cylinder 7

P0299 — quick answers

Is it safe to drive with P0299?

Drive only if essential. Limit driving to essential journeys until a garage has found why boost is low. If power collapses, you hear a loud hiss, or the engine management light flashes, stop and arrange recovery.

Can I fix P0299 myself?

Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage. Basic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.

Will P0299 fail my MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the fault is repaired and the light stays off. Clearing P0299 without fixing the boost fault is not a repair.

Fault-code identifiers are standard diagnostic facts. Their explanations and diagnostic guidance on this site are original editorial summaries, not reproduced SAE wording. MOT defect rules reflect the DVSA MOT inspection manual (2026). This page is general guidance for UK drivers, not a substitute for a professional diagnosis.