I have a 2003 Volkswagon Passat. I left the lights on all day so that the battery was entirely dead. The next day I got a friend to help me jump it. He put the cables on wrong and when we put them on the right way, the car wouldn't start. I had it towed to mechanic. They said they didn't know exactly what was damaged but the ECM was probably blown. They also said the electricity was running backwards and even if the ECM was replaced, all electric systems would start failing in a domino effect. They also called a local dealership to verify this. I assumed a car from 2003 would have fuses to prevent totaling your car by connecting jumper cables wrong but the mechanic said otherwise. Is there any reason I shouldn't call it a loss and junk the car?


closed as primarily opinion-based by Pᴀᴜʟsᴛᴇʀ2 Apr 13 '17 at 0:42

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  • Have you checked the fuses? – Zaid Apr 12 '17 at 16:03
  • Did you try to start it while hooked backwards? – agentp Apr 12 '17 at 18:57
  • yes unfortunately, would that mean it could be irreparable like they said? – Willem Apr 12 '17 at 19:41

If the existing battery was connected it is unlikely that you have done a level of damage that isn't worth fixing.

The two batteries fight each other creating a short circuit between them, it is highly unlikely that there would be a negative voltage reaching any ECU high enough to do any damage.

Depending on how long it was connected the wrong way the battery may survive and just need charging but the chances are it needs replacing. You would have also most certainly blown some fuses, look for some big 'mega' fuses connected directly to the positive cable.

  • okay ill take a look at the fuses. Is there any way to test to see if the problem is the battery without replacing the battery? – Willem Apr 12 '17 at 19:49
  • 1
    @Willem Take the battery to a place like Auto Zone or Advanced Auto Parts, and they will test the battery for free. – Unknown Zombie Apr 12 '17 at 20:19
  • you can rest assured the battery is shot. even a weak battery would have produced a nasty spark to let you know you hooked the cables backward – agentp Apr 13 '17 at 1:56

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