Jump start from hell


  1. I'm new to the site but not new to cars and my first post is pretty bad …I'm going to give you guys step by step of what i discovered ..

    our 2003 mini(AT base model) couldn't start for my girl after work so she decided to jump start it with cables her gf had ..she connected the cables wrong (as in neg to pos and pos to neg) …the jumper cables are now destroyed and cant be used(burnt)..she then decided to ask another friend for jump,did it the right way car started but now she told me the car steering is stiff like the car is shut off, i told her keep it running till i get there…when i arrive car was still running and steering was stiff so my first instinct is shut it of check fluids..i turn the key off position took the key out car was still running i immediately think ECM/ECU is fried …pop the hood i smell burning smell i disconnected the battery car shuts off ..i put my nose close to the ECM and i swear i smell burnt smell ..fluids all checked ok i decided to connect battery again to start it up once more ..as soon as i connected the battery all the lights on dash board lit up without the key being in and to be honest it acted exactly how if you place your key in the on position without starting the car ..now the car won't start but turns over very strong, at this point i had the car towed to the house ..when i got home i tried disconnecting battery for 10mins still won't start..so far i know used/rebuilt ecm is around 400-550 new one from dealer is 1400 …dealer said if ECM was bad the car won't start which is right car isnt starting but i found the car running after the second jump start which is now confusing me…can i get used ECM then take to dealer to get flashed OR a good friend has a scanner that works for mini could have him scan it..dealer also said it could be my Body Control unit (MAIN control unit)? different from ECM …ANY help you guys can offer will be great of what I need.. thanks

  2. Ok you mention the Body control unit, basically modern cars have computers all over them 'ECU – Electronic Control Unit' is just a generic term really.
    Early (mid 80's) electronic fuel injection cars only had one computer, which ran the engine. Modern cars have several, usually there is the Engine computer, body computer, Airbag/safety computer, ABS computer, Air con computer… it varies from one make to another.
    The Body Computer usually controls all the auxiliary stuff, dash mileage, alarm/immobiliser, lighting and the more 'cool' stuff like Bluetooth, follow me home lights, auto wipers etc etc

    Best thing to do is go back to basics, it might just be a burnt out short somewhere, check all the fuses and go from there. Plugging any diagnostic computer into it will show if the ecu's are dead, as it wont be able to talk to them.

    Any decent auto-electrician should be able to solve it for you for a lot less than a BMW dealer will charge.

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