Voltmeter Drain Testing

WARNING: DO NOT ATTEMPT THIS TEST ON A LEAD-ACID BATTERY THAT HAS RECENTLY BEEN RECHARGED.

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

NOTES:
- Many computers draw 10 mA or more continuously.
- Use an in-line ammeter between the battery positive or negative post and its respective cable.

1. Checks for current drains on the battery in excess of 50 mA with all the electrical accessories OFF and the vehicle at rest. Current drains can be tested with the following procedure:
a. Set ammeter to mA DC.
b. Disconnect battery terminal and momentarily touch cable to post.
c. Isolate circuit causing current drain by pulling out one fuse after another while reading the display. Current reading will drop when the fuse on the bad circuit is pulled.
d. Reinstall fuse and test components (including connectors) of that circuit to find defective component(s).

NOTE: Typically, a drain of approximately one amp can be attributed to an engine 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 alternator.

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 (for example, engine compartment, glove compartment, luggage compartment lamps) that do not shut OFF properly.

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