Here is a generic routine for finding the source of parasitic battery drain. WARNING!!! It will erase all data that is not stored in non-volatile memory.
The most common loss is of preset radio stations.
One BIG problem with this method is that modern vehicles have many devices which depend on being connected to the battery all of the time
in order to operate correctly. Therefore, it is recommended to only use an incandescent light or LOW impedance meter to perform this test. Otherwise, a lot of good components will end up getting replaced and you will be MAD at me...
Wrench for battery terminal
Low impedance meter like Klein MM700, or Fluke 114, 116 and 117 meters. (common digital multi-meters or a automotive test meter may work but tend to be high impedance meters which will show voltages even when poorly connected or even disconnected)
OR a 12 Volt incandescent test light from an auto parts store, or something like a brake light bulb with leads for testing NOTE: These instructions are written for meters. If a light is used, then consider the brightness of the light to be the relative voltage.
Fuse pulling tool
Gloves for chemical protection
Safety goggles for protection from acid splash (Because the battery can explode during this test, don't ask how I know!)
A clearly written circuit diagram for the vehicle being tested.
Optional but recommended tool:
Battery terminal cleaner brush from auto parts store (Do NOT use a brush without a shield to prevent splatter unless you are wearing goggles. Burned corneas really hurt a lot. Again, don't ask...)
Ground = the metal parts of the care that are connected to the negative (-) terminal of the battery
Lead = wires and probes or clips connected to a meter or light bulb
Cable = Big wire connected to the battery
DC = battery voltage (Direct Current) Confusing isn't it? Yep, I'm using current to define a voltage.
- With the key out of the ignition, and all doors closed and lights off (if there is a light over the fuse box, remove the bulb), and while wearing gloves and goggles during all steps ----
- Disconnect the Ground cable from the battery (Be sure it is the Ground cable because removing the other cable can cause sparking if the tool hits ground (any metal of the car).
- Set up the meter to measure DC volts and low impedance if available, and look at the lead's connections to be sure they are NOT in the current measuring sockets on the meter for this test. (OK, for those who understand the difference between the voltage and current settings on a meter, it would be a LOT easier to use the current setting for this test, BUT it is also a LOT easier to blow the meter's fuse or even the meter itself by connecting a lead in the wrong location.)
- Connect the meter or light between the battery's ground post or terminal (+) and the ground-cable. (If the light does not at least glow, you will need to use a meter.)
The meter will show some voltage. It is not important what the voltage is. If the voltage is stable, proceed to the next step. If the voltage is fluctuating, adjust the test leads on the battery and cable until the voltage becomes stable.
- Remove one fuse and watch the meter. If the voltage on the meter does not change, replace the fuse, and remove another. If the voltage on the meter changes, write down which fuse was removed and keep the fuse out but keep track of where it came from so you don't mix up the fuses when putting it back later.
- If there is still a stable (but different) voltage on the meter, pull the next fuse and repeat as necessary until the voltage on the meter becomes unstable or drops to zero.
- Determine which circuit the removed fuse(s) are connected to.
- Plug one of the fuses back in and then disconnect one device from the circuit the fuse is supplying.
- Watch the meter and follow the same steps which were used to find the parasitic drain's fuse above. (If the voltage changes or drops to zero, replace the device with a new one. If no change in voltage, reconnect the device and disconnect another device on that fuse's circuit.
- Repeat steps 8 & 9 until all drains are gone.
Edited to add the bit about low impedance meter setup and this note.