Battery (Parasitic) Load Test
PARASITIC LOAD TESTIf a battery requires recharging and no cause is evident (i.e., headlamps left: on, extended vehicle storage, etc.), the vehicle should be diagnosed for excessive current drain. Excessive current drain occurring while a car is parked (ignition switch off) can cause a discharged battery which could be improperly diagnosed as one which will not hold a charge. Current drain can be accurately checked using digital multimeter J 34029-A and two alligator clip-type jumper wires as follows:
1. Disconnect the negative battery cable.
2. Install a battery side terminal adapter (AC Delco ST- 1201 or equivalent) in the negative terminal of the battery.
3. Install a 3/8-16 nut with standard threads (16 UNC) and a clean metal washer on the negative battery cable terminal. Attach screw to assure a good electrical contact with the lead face on the cable for testing. Yellow or black finish nuts are generally nonconductive and should not be used.
4. Install high capacity ammeter and set to DC, mA and the 2,000 range.
Battery Drain Test Circuit:
5. With all lights, accessories, and the ignition switch off, connect the multimeter in series with the battery as shown.
6. A current draw of 50 mA or less (25 mA is normal) indicates that all lights and accessories are off and there is no unexplained current draw. It is necessary to wait for 7 minutes after connecting the multimeter in the test circuit before measuring current draw to allow the Electronic Level Control (ELC) to time out and turn off the ELC exhaust solenoid. Any momentary disconnection of the circuit will reset the ELC timer for another 7 minutes; therefore, it is essential to have good connections at all points throughout the above test.
Component Parasitics:
7. Once it has been determined that a parasitic drain in excess of 50 mA exists, a visual inspection of the vehicle should be conducted to determine the source of the drain. Check to see if there are any unwanted lights on, motors running or switches/relays activating. If no cause for the draw is immediately apparent, it may be possible to narrow in on the source by systematically removing fuses and circuit breakers, on by one, from the fuse panels. This should be done while monitoring the ammeter so that a disruption of the drain will be evident. Refer to Figure for and maximum parasitic loads for various vehicle components.
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