How to Troubleshoot a Subaru Outback Alternator

Written by lee sallings
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How to Troubleshoot a Subaru Outback Alternator
Use a digital meter on computerised circuits to prevent damage. (bio battery image by dinostock from

The alternator in your Subaru Outback is the heart of the charging system. Without it, the battery would quickly run out of power and the engine would stall. Understanding that the battery starts the car and that the alternator charges the battery and supplies the electrical power requirements of the car is the key to troubleshooting the alternator; troubleshooting this key component of the charging system may seem like a daunting task, but it turns out to be a relatively simple procedure that involves conducting a few simple tests.

Skill level:

Things you need

  • Digital volt/ohm meter (DVOM)

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  1. 1

    Turn your DVOM on and set it to read volts D/C. Attach the negative (black) lead on the DVOM to the negative battery terminal and the positive (red) lead on the meter to the positive battery terminal.

  2. 2

    Read the voltage displayed on the meter. It should be above 12.3 volts with the engine off and the ignition key in the "Off" position. If the battery voltage is less than 12.3 volts, charge the battery before testing the alternator. A discharged battery may cause the alternator in your Subaru to overcharge and may be a possible cause for alternator failure.

  3. 3

    Remove the positive DVOM lead from the battery and touch it to the charging post on the back of the alternator. The charging post is the metal screw that the large wire is bolted to on the back of the alternator. The voltage reading on the DVOM should be the same as that on the battery. If there is no voltage at the alternator, check the charging system fuse in the under-hood fuse block.

  4. 4

    Reconnect the positive DVOM lead to the positive battery terminal and start the engine. The voltage should now read above 13.5 volts. If the battery voltage is the same (or lower) with the engine running than it is with the engine off, replace the alternator.

Tips and warnings

  • Many of the circuits in modern cars and light trucks are computer-controlled. Use only a digital volt ohm meter to test the circuits in your car. An analogue meter will draw to much current and damage the low current circuits in your on-board computer.

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