A turbo rarely fails without warning. Here are the most common signs, what usually lies behind them and how urgently you need to act.
The car feels flat, especially uphill or when overtaking, and the revs climb slowly.
Not enough boost – worn bearings, sticking geometry, a failed actuator or a leak in the hoses or intercooler.
Get it diagnosed. If there’s a P0299 (underboost) code, check the hoses and vacuum system first.
Bluish smoke, especially when accelerating or after idling, with a smell of burnt oil.
Oil getting past the turbo seals into the exhaust or intake – worn bearings and piston rings, a blocked oil drain or high crankcase pressure.
Don’t keep driving for long – a diesel can run away on its own oil. Have the turbo checked as soon as possible.
A cloud of black smoke when you accelerate, sometimes with a loss of power.
An over-rich mixture – not enough air from the turbo, a boost leak, a dirty MAF sensor or an injector problem.
Diagnose the boost and fuel systems. The cause is often a hose or intercooler rather than the turbo itself.
A loud, piercing noise that rises with revs – different from a turbo’s normal faint whistle.
An unbalanced rotor, worn bearings, a wheel touching the housing or a boost leak.
Get it checked in time – if a wheel rubs the housing, fragments can end up in the engine.
A sharp metallic sound from the turbo area, especially under throttle.
The compressor or turbine wheel is rubbing the housing due to excessive shaft play, or a foreign object has entered the turbo.
Switch off the engine and don’t carry on. A disintegrating wheel can damage the intercooler and the engine.
The engine suddenly loses power and won’t rev past a certain point; the engine warning light comes on. Sometimes it’s fine again after a restart.
The ECU detects overboost (P0234) or underboost (P0299) – sticking geometry, a failed electronic actuator, solenoid or sensor.
Read the fault codes. Sticking geometry can often be fixed by cleaning and setting up, without replacing the turbo.
You need to top up oil between services with no visible leak under the car.
Worn turbo seals letting oil into the exhaust or intake.
Check the intercooler hoses for oil and have the shaft play inspected.
When the boost hoses are removed there is oil or oily residue inside.
A light oil mist is normal (from crankcase ventilation), but pools of oil mean a leak past the compressor-side seals.
When a turbo is repaired or replaced the intercooler must be cleaned – otherwise the oil goes straight into the new turbo and the engine.
The car uses noticeably more fuel with the same driving style.
The driver compensates for the lack of power with more throttle; the engine runs a less efficient mixture with low boost.
Keep an eye on consumption and have the boost pressure checked at your next service.
Power arrives later and later, and throttle response at low revs is sluggish.
Dirty or stiff VNT vanes, a worn mechanism or a poorly adjusted actuator.
Cleaning and setting up the geometry often makes the car respond like new again.
A large share of the cases where drivers suspect the turbo turn out to be something else: a split or disconnected boost hose, a leaking intercooler, a faulty boost control solenoid (N75), a vacuum leak, a bad boost pressure (MAP) sensor, a mass air flow (MAF) sensor, a blocked DPF or a stuck EGR valve.
Replacing a healthy turbo won’t fix the problem – and if the real cause (such as poor lubrication or a clogged particulate filter) remains, even a brand-new turbo will fail again. That’s why we always start with diagnostics.
Call us – we’ll tell you what the problem is likely to be and what the most sensible fix is, before you spend money you don’t need to.