The power train control module (PCM), or engine control unit (ECU), is a circuit board computer that stores information pertaining to different areas of your Mazda's engine. If your Mazda's check engine light or another malfunction indicator light illuminates, it is because of a signal the PCM received. The PCM will trigger the indicator light to illuminate to inform you there may be an issue with your Mazda. Occasionally, the information remains stored with your PCM, even after the issue has been fixed, and your indicator light may remain on until the PCM has been reset. Resetting your PCM will only take a few minutes.
Open your Mazda's bonnet.
Disconnect the "Negative" terminal clamp to your Mazda's battery. The negative clamp should be black and marked with a "--" symbol. The positive terminal should be red and marked with a "+" symbol.
Sit in the driver's seat of your Mazda.
Push down and release the brake pedal five times consecutively.
Reconnect the "Negative" terminal clam on your Mazda's battery.