P0299 fault code meaning and fix
P0299 means the turbo isn't making the boost pressure the engine computer has asked for. A split boost hose, a sticking turbo actuator or a faulty boost sensor is usually behind it, and we can find out which at your home or workplace.
The short answer
The official description for P0299 is Turbocharger/supercharger A underboost condition. The ECU has compared the boost it requested with the figure from the boost pressure sensor and found the real reading too low for too long.
Most cars still move with P0299 stored, though many drop into limp mode to protect the engine. A gentle trip home is usually fine, but pull over if you hear grinding or see clouds of blue smoke.
Symptoms that go with P0299
- Power fading under load, most noticeably uphill or on a slip road
- Limp mode, with the revs held down until the engine is switched off and restarted
- A louder whistle, hiss or whoosh as the turbo spools up
- Black smoke under acceleration, as there's too little air for the fuel going in
- The engine management light, sometimes joined by the glow plug light on diesels
- Fuel use creeping up because the engine works harder for the same pace
What causes P0299
| Cause | What you might notice | How it's confirmed |
|---|---|---|
| Split or loose boost hose | Hissing under load, oily residue at a joint | Smoke test |
| Leaking intercooler | Power slowly tailing off, oil mist around the cooler | Smoke test |
| Sticking turbo vanes or actuator | Power that comes and goes, often worse when hot | Live boost data and an actuator test |
| Faulty boost pressure sensor | The code sets with little real change in power | Sensor reading compared with requested boost |
| Split vacuum pipe or boost control solenoid (vacuum-operated turbos) | Slow to build boost from low revs | Vacuum and solenoid checks |
| Worn turbo | Siren-like whine, blue smoke, oil in the pipes | Diagnosis first, then a garage replaces the turbo |
Reading P0299 properly
P0299 is a generic code, so it means underboost on any make. Some scanners show it as P029900, where the two extra digits are a sub-code adding detail to the same fault. Its opposite number is P0234, the overboost code.
Freeze-frame data stored with the code records engine speed, load and temperature when it set. It separates a hose that only opens up at high boost from a sensor that always misreads, and an air flow code such as P0101 can point to a leak.
How P0299 gets fixed
Read the codes and live data
Requested and actual boost are compared with the engine under load, alongside the freeze-frame record.
Pressure-test the intake side
A smoke test fills the boost pipes and intercooler with visible smoke, so a split or loose joint gives itself away in minutes.
Repair the cause
A hose, clip, sensor or actuator is put right. Where it needs a new part, a garage fits it and we tell you exactly which part that is.
Clear and recheck
The code is cleared and boost is checked again to confirm it now matches what the ECU asks for.
What we can do about P0299
Smoke test, £120 + VAT
Smoke is fed into the intake and boost pipes under pressure, showing up splits and loose joints that are hard to spot by eye. It's the quickest way to rule a boost leak in or out.
Mobile diagnostics, £100 + VAT
We read every stored code and compare live boost with the ECU's request, then talk you through the result. If a garage needs to fit a part, you'll know which one before you go.
What does P0299 mean in plain English?
The turbo isn't delivering as much boost as the engine computer wanted, so the engine is short of air and the ECU cuts power to protect itself.
Is P0299 a serious fault?
That depends on the cause. A split hose is a cheap repair, but leaving it overworks the turbo, and a turbo that's wearing out can damage the engine if it fails completely.
Can I clear P0299 with a cheap code reader?
You can switch the light off, and the car may feel normal for a while. The ECU keeps watching boost pressure, so the code returns the next time the shortfall appears.
Does P0299 mean the same thing on every make?
Yes. It's a generic code and always means underboost. What causes it varies from car to car, and some makes store their own boost codes alongside it with extra detail.
How much does it cost to find the cause of P0299?
A smoke test is £120 + VAT and a mobile diagnostic is £100 + VAT, both carried out where the car is parked. You'll know what needs fixing before any money goes on parts.
Get your P0299 fault checked
Tell us the registration and when the power drops off, and we'll bring the smoke machine and diagnostic kit to your home or workplace.
More fault codes explained
Eccles, Manchester M30 0SF