Electrical Load Management
Electrical load management is designed to maintain battery voltage and covers more than load-shed. The body control module (BCM) will request increases in idle speed from the powertrain control module (PCM), when the vehicle is in park or neutral, as well as turn off loads in order to manage the electrical system and preserve the vehicle electrical power availability. The BCM 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 calculated battery temperature is below -15°C (5°F), the BCM institutes steps to control the load.
The BCM makes constant voltage measurements. If the BCM detects a low voltage steps are taken to control the load.
The BCM calculates the net charge rate on the electrical system by making constant voltage measurements and using the measurements to calculate the charge rate in amp/hours. If the BCM detects a negative charge rate for the battery, the BCM institutes steps to control the load.
The BCM 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 below:
| Function | Battery Temperature Calculation | Battery Voltage Calculation | Amp-hour Calculation | Action Taken |
|---|---|---|---|---|
| Idle Boost 1 Start | <-15°C (5°F) | - | - | First level Idle boost requested |
| Idle Boost 1 Start | - | - | Battery has a net loss of 0.6 AH | First level Idle boost requested |
| Idle Boost 1 End | >-15°C (5°F) | Battery has a net loss of less than 0.2 AH | First level Idle boost request cancelled | |
| Idle Boost 1 End | - | 14.0 V | Battery has a net loss of less than 0.2 AH | First level Idle boost request cancelled |
| Load Shed 1 Start | - | - | Battery has a net loss of 1.6 AH | Controlled outputs cycled OFF for 20% of their cycle |
| Load Shed 1 End | - | - | Battery has a net loss of less than 0.8 AH | Clear Load Shed 1 |
| Idle Boost 2 Start | - | - | Battery has a net loss of 5.0 AH | Second level Idle boost requested |
| Idle Boost 2 End | - | - | Battery has a net loss of less than 2.0 AH | Second level Idle boost request cancelled |
| Idle Boost 3 Start | - | - | Battery has a net loss of 10.0 AH | Third level Idle boost requested |
| Idle Boost 3 Start | - | <10.9 V | - | Third level Idle boost requested |
| Idle Boost 3 End | - | >13.0 V | Battery has a net loss of less than 6.0 AH | Third level Idle boost request cancelled |
| Load Shed 2 Start | - | - | Battery has a net loss of 12.0 AH | Controlled outputs cycled OFF for 50% of their cycle |
| Load Shed 2 End | - | - | Battery has a net loss of less than 10.5 AH | Clear Load Shed 2 |
| Load Shed 3 Start | - | <11.9 V | Battery has a net loss of 20.0 AH | Controlled outputs cycled OFF for 100% of their cycle, Battery Indicator or Battery Saver Indicator ON request sent |
| Load Shed 3 Start | - | <10.9 V | - | Controlled outputs cycled OFF for 100% of their cycle, Battery Indicator or Battery Saver Indicator ON request sent |
| Load Shed 3 End | - | >13.0 V | Battery has a net loss of less than 15.0 AH | Clear Load Shed 3 |
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 BCM checks the battery temperature, battery voltage and amp-hour calculations and determines if a different power management function should be implemented.
The highest loads on the electrical system are the resistance load of heating elements. The BCM controls the heating elements in the outside rear view mirrors, the rear window and the heated seats, either directly or by sending messages to the module controlling power to these devices.