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Battery Drain Test

WARNING: Do not attempt this test on a lead-acid battery that has recently been recharged. Explosive gases can cause personal injury.
CAUTION: To prevent damage to the meter, do not crank the engine or operate accessories that draw more than 10A.
NOTE: Amperage draw will vary from vehicle to vehicle depending on equipment package. Compare to a comparable vehicle for reference. No production vehicle should have more than a 50 mA (0.050 amp) draw. Many modules draw 10 mA (0.010 amp) or more continuously.
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 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 drain is still not located after checking all the fuses, it may be due to the generator.
  1. Ensure junction box/fuse panels are accessible without turning on interior and hood lights. Drive vehicle over 30 MPH for at least 5 minutes. Park vehicle and allow to sit with ignition off for at least 40 minutes to allow electronic modules to power down. Go to next step.
  2. Connect a fused jumper wire between negative battery cable and negative battery post. Disconnect negative battery cable from negative battery post, without breaking the jumper wire connection to prevent modules from resetting. Go to next step.
    NOTE: It is very important that continuity is not broken between negative battery post and negative battery cable when disconnecting battery cable or connecting ammeter. If continuity is broken, go to step  1 .
  3. Ensure ammeter is set to read milliamps with at least a 10-amp capability. Connect ammeter between negative battery cable and negative battery post. Remove fused jumper wire. Go to next step.
  4. If excessive current draw is present (50 mA or more), pull fuses from battery/central junction box one at a time and note any current drop when each fuse is removed. DO NOT reinstall fuses until test is complete. Go to next step.
  5. Check wiring diagrams for any circuits that run from battery without passing through battery/central junction box. Disconnect these circuits if current draw still exists. Repair appropriate circuits as necessary. See POWER DISTRIBUTION in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
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