Electrical Load Management

The PMM calculates the battery temperature, voltage and charging rate at all times while the engine is running. The BCM calculates the battery temperature by factoring in:
^ the current intake manifold air temperature compared to the last temperature recorded when the ignition switch was turned OFF
^ the current battery voltage compared to the last battery voltage recorded when the ignition switch was turned OFF
^ the length of time since the last battery temperature calculation

If the battery temperature is below set limits, the PMM institutes steps to control the load.

The PMM calculates the voltage of the battery by making constant measurements and using the measurements to calculate the true battery voltage. If the PMM detects a low voltage, the PMM institutes steps to control the load.

The PMM calculates the discharge rate, or draw, on the battery by making constant measurements and using the measurements to calculate the discharge rate in amp/hours. If the PMM detects a high current draw from the battery, the PMM institutes steps to control the load.

One of the highest loads on the electrical system is the resistance load of heating elements. The PMM controls the heating elements in the outside rear view mirrors and the rear window, as well as the heated seats, by controlling the relay coil controlling power to these devices




The PMM will either request an increase in the engine idle speed from the PCM or the PMM will turn off loads, called the load-shed function, in order to preserve the vehicle electrical system operation. The criteria used by the PMM to regulate this electrical load management are outlined.

Each load management function, either idle boost or load-shed, is discrete. No two functions are implemented at the same time.

During each load management function, the PMM checks the battery temperature, battery voltage and amp-hour calculations and determines if the PMM should implement a different power management function.