2008 Pontiac Grand Prix Owner's Manual - Page 138

Electric Power Management The vehicle has Electric Power Management (EPM) that estimates the battery's temperature and state of charge. It then adjusts the voltage for best performance and extended life of the battery. When the battery's state of charge is low, the voltage is raised slightly to quickly put the charge back in. When the state of charge is high, the voltage is lowered slightly to prevent overcharging. If the vehicle has a voltmeter gage or voltage display on the Driver Information Center (DIC), you may see the voltage move up or down. This is normal. If there is a problem, an alert will be displayed. The battery can be discharged at idle if the electrical loads are very high. This is true for all vehicles. This is because the generator (alternator) may not be spinning fast enough at idle to produce all the power that is needed for very high electrical loads. A high electrical load occurs when several of the following loads are on: headlamps, high beams, fog lamps, rear window defogger, climate control fan at high speed, heated seats, engine cooling fans, trailer loads, and loads plugged into accessory power outlets. EPM works to prevent excessive discharge of the battery. It does this by balancing the generator's output and the vehicle's electrical needs. It can increase engine idle speed to generate more power, whenever needed. It can temporarily reduce the power demands of some accessories. 3-22 Normally, these actions occur in steps or levels, without being noticeable. In rare cases at the highest levels of corrective action, this action may be noticeable to the driver. If so, a Driver Information Center (DIC) message might be displayed, such as Battery Saver Active. If this message is displayed, it is recommended that the driver reduce the electrical loads as much as possible. See DIC Warnings and Messages on page 3-67. Battery Run-Down Protection The vehicle has a feature to help prevent the battery from draining in case the interior, trunk, or underhood lamps are accidentally left on. If any of these lamps are left on while the ignition is in LOCK/OFF, they will automatically turn off after 10 minutes. The lamps will not come back on again until any of the following are done: • The ignition is turned to ON/RUN or ACC/ACCESSORY. • The interior lamps control is turned completely to the right, then back slightly to the left. • Open, or close and reopen, a door that is closed. If the vehicle has less than 15 miles (25 km) on the odometer, the battery saver will turn off the lamps after only three minutes.