The check engine light illuminates on a Mazda to indicate the powertrain control module has detected a problem in the engine or transmission of the vehicle. The powertrain control module is a computer that manages the vehicles fuel injection, firing and emissions, according to Repair Pal.
The check engine or malfunction indicator light is on the instrument panel of the vehicle. The engine control module stores a code for the malfunction responsible for illuminating the light. Mechanics use a scanning tool to retrieve the code. Each code has its own list of possible causes.
Some Mazdas, from the late 1990s to the mid 2000s, have a check engine light that illuminates at 80,000 miles without storing a code in the module, says a Wikipedia page on check engine lights. Mazda uses this as a reminder that routine maintenance of the vehicle requires replacement of the oxygen sensors.
The design of the check engine light causes it to illuminate when the ignition switch is in the on position before the car is started. This allows the driver to know that the light is functioning properly. Unless the ECM has sensed a problem, the light turns off once the engine starts.
Repair Pal reports that in 2001 to 2010, Mazda vehicles with a 3.0 liter V-6 engine, an engine misfire caused by damage to the wires connecting the PCM to the fuel injectors causes illumination of the malfunction indicator light. The problem occurs after 68,000 miles. Replacing the fuel injector wiring harness corrects the issue.