Drain Test

WARNING: DO NOT ATTEMPT THIS TEST ON A LEAD-ACID BATTERY THAT HAS RECENTLY BEEN RECHARGED. FAILURE TO FOLLOW THESE INSTRUCTIONS WILL RESULT IN PERSONAL INJURY.

CAUTION: Do not crank the engine or operate accessories that draw more than 10 A. You could blow the fuse in the meter.

NOTE
^ Many computers draw 10 mA or more continuously.
^ Use an in-line ammeter between the battery negative terminal and its respective cable.

Check for current drains on the battery in excess of 50 milliamps with all the electrical accessories off and the vehicle at rest. Current drains can be tested with the following procedure.

1. Disconnect battery ground cable.
2. Connect black lead on ammeter to negative (-) post on battery.
3. Connect red lead on ammeter to battery ground cable.
4. Isolate circuit causing current drain by pulling out one fuse after another while reading the display.
5. Current reading will drop when the fuse on the relevant circuit is pulled.
6. Reinstall fuse and test components (including connectors) at that circuit to find a damaged component(s).

Typically, a drain of approximately one amp can be attributed to a compartment lamp, glove compartment lamp, or luggage compartment lamp staying on continually. Other component failures or wiring shorts may be located by selectively pulling fuses or disconnecting fuse links to pinpoint the location of the current drain. When the current drain is found, the meter reading will fall to an acceptable level. If the short is still not located, after checking all the fuses and fuse links, the drain may be due to the generator.

The current reading (current drain) should be less than 0.05 amp. If it exceeds 0.05 amp, it indicates a constant current drain which could cause a discharged battery. Possible sources of current drain are vehicle lamps (underhood, glove compartment, luggage compartment, etc) that do not shut off correctly.

If the drain is not caused by a vehicle lamp, remove the fuses from the central junction box, one at a time, until the cause of the drain is located. If drain is still undetermined, remove fuses from the battery junction box, one at a time to find the problem circuit.

Electronic Drains Which Shut Off When the Battery Cable is Disconnected.
1. Repeat steps 1 through 6 of the ammeter drain testing.
2. Without starting engine, turn ignition ON for a moment and then off. If applicable, wait one minute for the illuminated entry lamps to turn off.
3. Connect the ammeter and read the current.

The current reading (current drain) should be less than 0.05 amp. If it exceeds 0.05 amp after a few minutes, and if this drain did not show in previous tests, the drain is most likely caused by a malfunctioning electronic component. As in previous tests, remove the fuses in the central junction box one at a time to locate the problem circuit.