BMW Valvetronic explained: how BMW engines breathe without a throttle
Valvetronic lets BMW engines control their power with the intake valves instead of a throttle. How it works, why it saves fuel, which engines use it and what can go wrong.
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BMW Valvetronic is one of the most clever technologies in modern BMW petrol engines. Instead of using a throttle valve to control how much air enters the engine, it changes how far the intake valves open. The result is better fuel economy and a quicker throttle response.
In this article we explain how BMW Valvetronic works, why it was developed, which engines use it, its benefits and the faults that owners should know about.
The problem with a throttle valve
In a traditional petrol engine, the driver controls the power with a throttle valve: a flap in the intake that opens and closes. When you press the accelerator a little, the throttle opens a little and lets in only a small amount of air.
This system works, but it is not efficient. At part throttle, the pistons have to suck air past an almost closed flap, which creates a vacuum in the intake. This costs energy, called pumping losses, and these losses are largest exactly when we drive most of the time: at low and medium load.
Engineers have long looked for ways to reduce pumping losses. Diesel engines do not use a throttle in the same way, which is one reason why they are efficient at part load.
BMW's answer for petrol engines was Valvetronic: control the air directly at the intake valves, so the throttle flap can stay open.
How BMW Valvetronic works
Valvetronic is a fully variable valve lift system for the intake valves. Instead of a fixed lift, the intake valves can open just a tiny amount or fully, and anything in between.
The system uses an extra shaft in the cylinder head, called the eccentric shaft, turned by a small electric motor. Between the camshaft and the valves there are intermediate levers. When the electric motor turns the eccentric shaft, it changes the position of these levers and therefore how far the valves open.
The engine computer controls the motor continuously. At idle and light load, the valves open only slightly; under full load, they open fully. The amount of air entering the engine is controlled by the valve lift itself, so the throttle valve can stay open in normal driving.
The throttle is still present, but mainly for special situations, such as emergency operation and certain engine functions. Valvetronic works together with double VANOS, which controls the timing of the camshafts.
History and engines with Valvetronic
BMW introduced Valvetronic in 2001 on the N42 four-cylinder engine, used in the 3 Series compact and saloon. It was one of the first systems of its kind in series production.
The technology was soon extended to six-cylinder engines. The N52 straight-six of 2004 used Valvetronic together with a lightweight magnesium-aluminium block. Later engines, such as the turbocharged N55 and the modern B48 and B58 from BMW's modular engine family, also use it.
Valvetronic was also used on some V8 and V12 engines and on engines from MINI, which is part of the BMW Group.
Not all BMW engines have Valvetronic. Some high-performance M engines, for example, use other technologies to achieve their character at very high engine speeds.
The benefits
Valvetronic brings several advantages:
- Lower fuel consumption. By reducing pumping losses, Valvetronic engines use less fuel, especially in town and in relaxed driving. BMW quoted savings of around ten per cent when the system was introduced.
- Quicker response. The air is controlled directly at the valves, so the engine reacts very quickly to the accelerator pedal.
- Smoother idle. Very small valve lifts at idle create a fast, controlled air flow that helps clean combustion.
- Lower emissions, thanks to better control of combustion and reduced fuel consumption.
For drivers, Valvetronic is mostly invisible. The engine simply feels responsive and economical.
Common Valvetronic faults
Valvetronic is generally reliable, but it adds parts that can wear or fail with age:
- Valvetronic motor. The electric motor that turns the eccentric shaft can fail. Symptoms include rough running, loss of power and fault messages.
- Eccentric shaft sensor. This sensor tells the computer the exact position of the shaft. On some engines it can fail, often because of oil leaks from nearby gaskets reaching its connector.
- Oil leaks from the Valvetronic motor seal or the valve cover gasket, which can affect the sensor and the wiring.
- Wear of the intermediate levers on very high-mileage engines, especially if the oil was not changed regularly.
Typical symptoms of a Valvetronic problem are a rough idle, hesitation, a check engine light and the engine running in an emergency mode with reduced power. A diagnostic scan usually shows which part is at fault.
How to keep Valvetronic healthy
Like VANOS, Valvetronic depends on clean oil and well-sealed engine parts.
- Change the oil regularly with the oil specified by BMW. Dirty oil and sludge can harm the levers and the shaft.
- Fix oil leaks quickly, especially around the valve cover, so oil cannot damage the sensors and connectors.
- Use quality parts for sensors and gaskets.
- Take warning lights seriously. A small fault, such as a sensor, is cheaper to fix than the damage caused by running in emergency mode for a long time.
Valvetronic is one of the reasons why modern BMW petrol engines combine strong performance with good economy. With proper care, it works quietly in the background for many years.
Valvetronic at a glance
| Item | Details |
|---|---|
| Introduced | 2001, N42 four-cylinder |
| Principle | Fully variable intake valve lift instead of throttle control |
| Main parts | Eccentric shaft, electric motor, intermediate levers, sensor |
| Engines | N42, N52, N55, B48, B58 and others |
| Benefits | Lower consumption, quicker response, smoother idle |
| Common faults | Valvetronic motor, eccentric shaft sensor, oil leaks |
Frequently asked questions
What is BMW Valvetronic?
Valvetronic is BMW's fully variable intake valve lift system. It controls the engine's air intake with the valves instead of the throttle valve, which saves fuel and improves response.
Which BMW engines have Valvetronic?
Many BMW petrol engines since 2001, including the N42, N52, N55 and the modern B48 and B58 engines.
What are the symptoms of a Valvetronic problem?
Rough idle, hesitation, loss of power, a check engine light and the engine running in an emergency mode are typical symptoms.
Is Valvetronic the same as VANOS?
No. VANOS changes the timing of the camshafts, while Valvetronic changes how far the intake valves open. Many BMW engines use both systems together.
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