The stepper motor – how it works, why it exists and why it breaks down?

19 Jun 2020

The stepper motor failure is a common problem with modern cars. It is a small and usually not very expensive, but troublesome part. Especially when the symptoms caused by its failure are diagnosed incorrectly.

How does it work?

The stepper motor is responsible for regulating the idle speed. It is present in vehicles with petrol engines with an injection supply system. It controls the air flow to the engine, based on a few constantly recognised parameters. It prevents the falling of the number of revs below the minimum.

The operation of the stepper motor is regulated by the ECM which stands for the Electronic Control Module. It provides the motor with pulses, the so-called “steps”, which allow for altering the throttle deflection angle. The ECM “sees” what information is passed to the motor as it uses the coolant temperature sensor, crankshaft position sensor and the value of the manifold absolute pressure (MAP) in the suction manifold. It focuses on the information regarding: engine temperature, RPM and pressure.

Uneven idle stepper motor failure

Each component involved in the operation of the engine is susceptible to contamination, and the stepper motor can also become contaminated due to residue accumulation. The solution to this problem is often limited to simply taking it out and cleaning it, cleaning the throttle, and reassembling them in place. In newer vehicles, cleaning and lubricating the motor more and more frequently doesn’t guarantee the desired result. It may happen that after carrying out these steps, the motor starts operating, but its range is too small.

The stepper motor failure can also result from electrical components. E.g. a burned plug or one of the drivers. Replacing these elements in today’s conditions generates so small savings without providing any guarantee of success that most mechanics reject such solutions. Therefore, the most effective is replacing the motor with a new one. It is because the prices of stepper motors on the aftermarket aren’t particularly high.


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