BMW has over the years, utilized a system called Valvetronic on their engines, to improve overall engine efficiency and control the idle speed. These engines did not require a throttle body to control the idle, but still have one as a backup in the event of the Valvetronic failure. The basic principle of this system was to control the valve lift through a variable motor control and rocker arm assembly. Limiting the amount of lift on the inlet valves reduces the air flow, and reduces the engine idle speed.

Early systems suffered from a failing DC motor, and the insulation failed internally. The system then reverted to using the throttle body for idle control.

This system requires adaptation after a depleted battery, or battery replacement. This often manifests as an emissions failure, for no apparent reason. On resetting the Valvetronic system adaptions, via a scan tool, the idle and emissions would return to normal.

To accurately monitor the position of the system, an eccentric shaft was fitted, with a sensing module at the front end of the shaft.

Later systems were developed, with a smaller motor. These incorporated 5 internal position sensors. There are 3 for rough position, and 2 for fine position control. The numerous sensors make it a more refined system. On initial testing, it looks like a 3-phase motor is fitted.

The step controller is a DC motor with one supply and two controlled grounds, for direction control. The motor has a single 5-volt reference input, 1 ground connection, and 5 signal lines for position control.

When a fault code 2DD6 is present, it is usually a faulty stepper motor, or a worn shaft component. This may require the complete Valvetronic system replacement. But please make sure the components have the same part numbers, as there are multiple versions of this system.

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