How do you know if your pcm is bad in a 1999 Mazda millenia?

To determine if the PCM (Powertrain Control Module) is bad in a 1999 Mazda Millenia, check for common symptoms such as persistent check engine lights, erratic engine behavior, or failure to start. You can also use an OBD-II scanner to retrieve any diagnostic trouble codes, which may indicate PCM issues. Additionally, inspect the wiring and connectors for damage or corrosion, as these can affect PCM performance. If other components are functioning properly and codes point to the PCM, it may need to be replaced.