PWM

📖 YOUCANIC Automotive Glossary

PWM (Pulse Width Modulation) is an electronic control technique where the ECU rapidly switches a circuit on and off at a fixed frequency, varying the percentage of time the signal is ON (duty cycle) to control the effective power delivered to a component. Rather than needing a variable voltage supply, PWM achieves proportional control using simple on/off switching. For example, at 25% duty cycle, the component receives 25% of maximum power; at 75% duty cycle, it receives 75%. Because the switching frequency is very fast (typically 100-1000 Hz), the component responds to the average power level rather than pulsing on and off individually.

PWM is used extensively throughout modern vehicles: fuel pump speed control (higher duty cycle = more fuel delivery), cooling fan speed modulation (variable speeds instead of just on/off), idle air control, EVAP purge valve flow rate, VVT solenoid oil flow, turbo wastegate position, LED dimming, and blower motor speed control. In live data, PWM-controlled components show their commanded duty cycle percentage. The YOUCANIC UCAN-II displays duty cycle values for supported actuators, helping diagnose whether the ECU is commanding the correct output. If the ECU commands 50% duty cycle but the component does not respond proportionally, the issue is in the component or its wiring, not the ECU’s control strategy.