Question about 2001 Mitsubishi Galant

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P1603 Battery Backup Error

My car keeps giving me error P1603 - Battery Back up. I've had the ECU replaced, but the problem persists. Any tips for diagnosing or solving the problem?

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  • weffey Oct 12, 2008

    My guy and I feel like a bit of an idiot actually. The first thing we did when we got the car a few months ago was check all the fuses and replaced the pair that was blown. I came across another question on here that had identical symptoms to the ones we were experiencing and after a bit of digging, found out that the fuse that controls all the interior lights, power locks, idle, etc also controls the power supply to the ECU. We pulled the fuse again, and it was quite noticeably blown.

    We replaced the fuse, and all of our problems have gone away.



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There is a power supply to the ecu that is missing either permanantly or interrmitently, it may be as simple as a fuse, or it may have a bad connection in a loom plug or a broken wire...

Posted on Oct 12, 2008

  • Damian
    Damian May 09, 2014

    Pull the yellow case up and pull the fuses out. if you just try to usee a test light to check both sides of the fuse it will give you false results. Damian Southern Tier Auto Sprinville



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