Handbook 652 Body Electrical Diagnosis Other Voltage Sources Sensors used in ECU controlled systems such as TCCS and ABS produce an AC voltage that the ECU uses to determine RPM, or other operating conditions. Noise filters are capacitors which act as voltage “ accumulators ” to dampen sudden voltage changes. The ignition coil uses magnetic induction to step up the 12V battery voltage into the KV (thousands of volts) necessary to fire the spark plug. 10 Technical Training