Car systems
Turbo: how it works and what fails
The turbo uses the exhaust gases to spin a turbine that compresses the intake air, so more air gets in and the engine makes more power from the same displacement. Its faults show up as a loss of power, whistling, smoke and the limp mode the computer turns on to protect it.
Reviewed by Daniel Morales, founder of Reprorace SL, on
How it works
The exhaust gases spin the turbine, joined by a shaft to the compressor on the intake side; the shaft turns at more than 100,000 rpm and is lubricated and cooled by the engine oil. Compressed air heats up, so it goes through the intercooler before entering the engine.
The computer controls the boost pressure with the wastegate or with the variable geometry vanes and watches it with a boost pressure sensor. If the actual pressure strays from the requested one, it stores a code (P0299 for underboost, P0234 for overboost) and limits the power.
The most common faults
- Hoses and boost leaks: a loose or split hose lets the compressed air escape: whistling, lack of power and P0299.
- Seized variable geometry: carbon jams the vanes; it is typical of diesels driven mostly in town.
- Actuator or solenoid valve: the wastegate or geometry control does not respond and the turbo underboosts or overboosts.
- Lubrication: old oil or a low level damage the shaft: play, metallic noise and oil consumption with blue smoke.
- Boost pressure sensor: a false reading makes the computer limit the power even though the turbo is fine.
A guide, most likely first: a repair shop confirms the diagnosis of each car with its own data.
Symptoms that can come from this system
Turbo whistle when accelerating: when it is normal and when not
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Car loses power: what limp mode is
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Blue smoke from the exhaust: the engine is burning oil
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Black smoke from the exhaust: causes and what to do
Check without hurry
Car jerks when accelerating: causes and what to do
See a garage soon
The most relevant trouble codes
- P0299Turbocharger/supercharger A: underboost
- P0234Turbocharger/supercharger A: overboost
- P0033Turbocharger/supercharger bypass valve A, control circuit: malfunction
- P0034Turbocharger/supercharger bypass valve A, control circuit: signal low
- P0045Turbocharger/supercharger boost control A, circuit open
- P0046Turbocharger/supercharger boost control A, circuit: range/performance
- P0047Turbocharger/supercharger boost control A, circuit: signal low
- P0048Turbocharger/supercharger boost control A, circuit: signal high
- P0236Turbocharger/supercharger boost sensor A, circuit: range/performance
- P0237Turbocharger/supercharger boost sensor A, circuit: signal low
- P0238Turbocharger/supercharger boost sensor A, circuit: signal high
- P0243Turbocharger/supercharger wastegate actuator A: malfunction
- P2263Turbocharger/supercharger A boost system: performance
- P2563Turbocharger boost control position sensor A, circuit: range/performance
Generic OBD-II/EOBD codes; each manufacturer adds its own. The same symptom can come from another system.
Code blocks of this system
See what your car is saying, system by system
The ECO-LITE plugs into the OBD port and shows the codes and live data your car publishes on your phone, explained; when needed, you share the session with your repair shop.
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Frequently asked questions
Can I keep driving with the turbo in limp mode?
You can drive calmly to a repair shop if there is no heavy smoke, metallic noise or oil light. Pushing the engine can make the fault worse.
Should I wait before turning off the engine?
After a demanding drive, a few seconds at idle help the oil cool the turbo. In normal use, nothing more is needed.
Which live data help with the turbo?
The requested boost pressure against the actual one, the air flow and the actuator position. If the actual pressure does not reach the requested one under load, there is a leak or a control that does not respond.