Battery Electrical Drain/Parasitic Load
BATTERY ELECTRICAL DRAIN DIAGNOSISIf the vehicle exhibits a low or dead battery after an overnight period, or discharges over a period of 2 or 3 days, the electrical system should be checked for an excessive electrical drain. This is referred to as Parasitic Load Drain.
If a battery needs recharging and no cause is evident, check the vehicle for excessive parasitic load drain.
One or more on-board solid state control modules, such as the PCM, may at some time, exhibit a failure mode that causes a high parasitic drain on the vehicle's battery. When the battery is disconnected to install an ammeter, etc., the excessive current drain may not occur once the circuit continuity is restored. Even though cycling the ignition key to the ON and then to the OFF position may cause such a drain to reoccur, there may be drains that will not reoccur unless the vehicle systems are reactivated in a road test. Since the ignition switch must not be rotated to the ACCESSORY, ON or START position with an ammeter installed between the battery terminal and the battery cable, a current drain test tool must be used as described in the following procedures. Before starting this procedure, ensure that the ignition switch is in the LOCK position, all electrical accessories are turned OFF and the doors are closed.