Turbo underboost on Mini Cooper S — PCV diaphragm leak and charge pipe splits are the typical causes.
Mini P0299 — Turbo underboost on Mini Cooper S — PCV diaphragm leak and charge pipe splits are the typical causes. Typical UK independent garage cost: £180–£1400.
What actually causes P0299 on a Mini
On Prince-engine Cooper S (N14/N18), P0299 is almost always a torn PCV diaphragm or a split charge pipe — the same boost leak story as the 1.6 THP Peugeot. On the BMW B48-powered F56 Cooper S, P0299 is rarer and typically a wastegate or diverter valve issue. Always smoke-test before condemning the turbo.
Mini engines that log P0299
- N14 1.6 turbo (R56 2007–2010)
- N18 1.6 turbo (2010–2014)
- B48 2.0 turbo (F56 Cooper S)
How we diagnose P0299 on a Mini
- Smoke-test the full intake from turbo outlet to inlet manifold
- Inspect PCV diaphragm on cam cover (Prince classic failure)
- Check charge pipes for cracks and connector seal damage
- On F56 B48, test diverter valve and wastegate solenoid
- Replace cam cover assembly with genuine BMW/Mini part if PCV failed
The common misdiagnosis to avoid
Don't replace the turbo on a Cooper S before smoke-testing — PCV cam cover replacement (£250) fixes the majority of Prince P0299 codes.
Mini P0299 repair cost in the UK
Expect £180–£1400 including parts and labour at an independent garage. Main-dealer quotes on Mini are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Bob's workshop tip
Prince engines: PCV cam cover failure + charge pipe split account for nearly all Cooper S P0299 codes — the turbo itself is rarely the actual fault.
Codes usually seen alongside P0299 on Mini
- P0234
- P132B
- P0171
Symptoms drivers report with P0299
- Loss of power above 2,000–2,500 RPM — car feels flat overtaking on the motorway
- Limp mode kicks in at 3,000 RPM, resets after a key cycle, then returns within 10 miles
- Whistling from engine bay under load — split intercooler pipe or Y-piece
- Black smoke or fuel smell from the exhaust on diesels — VNT stuck open, over-fuelling
- Paired codes: P0234 (overboost, VNT stuck closed), P0299 with P0401 (EGR + boost overlap), P0299 with P132B (turbo boost control)
Repairs that clear P0299
- Smoke-test the boost system first (cheap and finds most causes)
- Clean VNT vanes with rocker-arm actuation
- Replace boost sensor
- Replace turbo as last resort
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0299 guide.