Tech Tip: Subaru Parasitic Battery Draw

Tech Tip: Subaru Parasitic Battery Draw

This bulletin provides the diagnostic procedure when checking for excessive battery draw for any Subaru model. Prior to beginning test, be certain the vehicle battery is fully charged and that the battery posts and cable ends are free of corrosion, dirt, sealer and in good condition ....

This bulletin provides the diagnostic procedure when checking for excessive battery draw for any Subaru model.

Prior To Beginning Test:

  • Be certain the vehicle battery is fully charged.
  • The battery posts and cable ends are free of corrosion, dirt, sealer and in good condition.
  • Be sure to record the customer’s radio station and satellite radio station pre-sets as they will be lost during the test, along with any seat memory settings.
  • You may not use an aftermarket 9V memory device in the power outlet to retain any ECU memory.
  • Any aftermarket accessories will also need to be disconnected. These items will affect the test results and may cause false readings or misdiagnosis.

Items Required For Test:

  • Pen and paper for recording radio and satellite radio pre-sets;
  • Digital volt ohmmeter;
  • 10 mm wrench; and
  • 16-gauge bypass wire, about 12 inches long, with proper securing attachments at each end.

Test Procedure:

  1. Remove the battery negative cable.
  2. Connect one end of the bypass wire to the battery’s negative post, then connect the other end to the negative battery cable end. Simply wrapping then twisting the stripped back ends of the bypass wire around the post and terminal will be sufficient. Reinstall the negative cable on the battery post
  3. Wait five minutes before proceeding to the next step. This will allow the system voltage to stabilize. During this time, be sure the glove box door, trunk, tailgate and all vehicle doors are closed and their corresponding lamps are off. Also, be sure that the head lamps, fog lamps and all switches are off. The ignition key needs to be removed, and the doors must be locked (make sure not to lock the keys in the car). Remove the negative battery cable, making sure the bypass wire has not lost contact. If contact is lost, you will need to restart at Step 2.
  4. Make sure your voltmeter is set to milliamp (mA) setting. Connect the test leads of your voltmeter to the negative battery cable and the negative battery post. Remove the bypass wire you installed in Steps 2 and 3 and measure the current draw.
  5. After the five-minute stabilization period, the measured draw should be a maximum of 150 mA. This maximum draw value is read with the key out of the ignition switch.
  6. If your results are greater than the above specification, further diagnosis will be necessary to determine the source of the excessive current draw. This should be done using normal electrical circuit testing until the source of this excessive draw is determined and repaired.
  7. After confirming the repair, the customer’s radio presets and clock time should be reset properly.

Technical service bulletin courtesy of ALLDATA.

For additional information, visit

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