P2579: Turbocharger/Supercharger Speed Sensor A Circuit Range/Performance
Do not keep driving
Worth stopping for, even though the car may feel only slightly flat. This code can mean the turbocharger is genuinely spinning faster than it was built to survive, and that is a failure measured in seconds rather than months when it comes — the compressor wheel can break up and send debris into the engine. Heavy throttle is the thing to avoid; gentle, low-load driving to somewhere it can be looked at is reasonable, and a recovery truck is not an overreaction.
The likeliest real cause is a leak, not the turbocharger. The engine asks for a boost pressure and pushes the turbo harder until it gets it — so if air is escaping from a split hose, a loose clamp or a leaking intercooler, the turbo just spins faster and faster chasing a pressure it can never reach. That is a cheap repair that prevents an expensive failure.
Ask for the charge air system to be pressure-tested before anything is replaced. That covers every pipe, hose and clamp between the turbo and the engine, it is quick, and it is where this code usually comes from. Replacing the speed sensor without doing that can clear the warning while leaving the turbocharger still overspeeding — the worst possible outcome.
If the turbo has been overspeeding for a while, ask for the shaft to be checked for play and the compressor wheel for damage.
What this code means
The turbocharger speed signal is electrically valid and does not make sense — a speed that does not correspond to what the engine is doing, or one outside the range the module will accept.
This code has two completely different meanings, and telling them apart is the whole job. Either the sensor is misreporting, or the turbocharger really is spinning at a speed it should not be. The first is a cheap repair. The second is a turbocharger a short time away from destroying itself, and it should be treated as the live possibility until it has been excluded.
Here is the mechanism that makes genuine overspeed common enough to worry about, and it is the single most useful thing on this page. The module does not command turbocharger speed. It commands a boost pressure and adjusts the turbo until the manifold reports that pressure. So if air is escaping between the compressor and the engine, the module responds to the shortfall by driving the turbocharger harder — and it will keep driving it harder, because from where it is looking the pressure target simply is not being met. A split intercooler hose, a popped charge pipe, a failed clamp or a leaking intercooler therefore does not just cost boost. It makes the turbocharger spin faster and faster in pursuit of a pressure it can no longer reach, and that is exactly the condition the speed sensor exists to catch.
What the driver notices is almost nothing. A boost leak feels like mild flatness — the sort of thing people put up with for weeks. The turbocharger meanwhile is running past its design speed on every full-throttle pull. This is why the code is marked as one to stop for: the symptom badly understates the risk.
So the order of investigation is the reverse of the intuitive one. Do not start at the sensor:
- Pressure-test the charge air system first. Everything between the compressor outlet and the inlet manifold — the intercooler, its hoses, every clamp and joint. This is where a genuine overspeed comes from, it is the cheapest thing on the list, and finding a split hose here explains the code completely.
- Then the boost control itself. Vanes stuck closed, a wastegate that is not opening, or an actuator that has lost its calibration will all overspeed a turbo — the same fault family as P2563, P2598 and P2599, and worth reading alongside this.
- Then the exhaust restriction question. A blocked particulate filter raises back pressure and changes what the turbine has to do to deliver a given boost.
- Only then the sensor. A sensor reading high when nothing else agrees is a real possibility, but it is the last one to accept, not the first — because accepting it wrongly means clearing the code on a turbocharger that is still overspeeding.
A turbocharger that has already been overspeeded needs inspecting, not just clearing. Check the shaft for play and the compressor wheel for rubbed tips or damaged blades. Damage there means the failure has already started.
Likely causes
Start here
- Boost leak in charge pipework · moderate
- Split or disconnected intercooler hose · easy
- Carbon build-up seizing the turbocharger vanes · specialist
- Faulty turbocharger speed sensor · moderate
Less common
- Wastegate stuck open or closed · specialist
- Blocked diesel particulate filter · specialist
- Worn turbocharger bearings · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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