I just pulled out my 1999 A6 Avant 2.8L, car is mint. Asked my friend to attach the booster pack, but placed the neg. on the positive, & the other way around. The battery terminal sparked, i.e. voltage spike I believe. Tried to start the car, it turned over & 5 to 10 seconds later turned off. Check engine on now, and kinda acting like the security immobilizer, preventing car to start. I checked the 40 amp fuse next to ECU in engine compartment & looks ok, not broken Nor looks damaged. There is a relay there, but dont have a spare & need to take cover off to get relay number. Now my feeling is the ECU jumped? Is there a Relay or fuse that would go before the ECU? Any ideas thoughts or ideas to repair without going the ECU Route!!!! Thanks In Advance. Banacek

 

You may have damaged the negative battery cable on your car. Try jumping the car with the negative battery cable from the jumper battery attached to a good ground on the engine. The positive cable will be attached to the positive posts on both batteries. If the car starts replace your negative battery cable.

 

I will give that a try!!!! So basically connect the positive like usual, but ground the negative from the booster to the car. Correct? If the car starts, what if the check engine light stays on, then change the negative terminal? Thanks for the tip, will give it a try. Thanks, banacek:d

 

I just tried to boost it with the booster pac, & nothing at all!!!! I am going to try & charge the booster pac up. I did get a small spark when i grounded it to a bolt on the body, but in the meantime not even enough to turn the lights on!!!

 

YIKES, had a friend do that to his lexus... he just ended up replacing the ICM and a few random fuses and it works.. good luck

 

Tried to start it by grounding the booster pack to the car, & not the negative terminal. Cant get it to start that way at all. I tried to the terminal & it starts then turns off again like before. Check engine comes on & engine turns off? Any other ideas, maybe a relay or fuse for the security system or is the ecu fired? Is there a safety measure so the ecu does not burn out? Any more info is much appreciated. Thanks

 

Hey mylan, thanks for the tip!!!! Moral of the story is turn your phone off when working on your car @ 7 am!!!! & tell the girlfriend to stop checking in & let it go straight to voicemail!!!!

 

I would try & get the battery charged up to full capacity before going any further. The car needs to have good voltage to start out with.
Another thing , try & communicate with ecm with a scanner.

 

I charged the battery up completely, turned it over & it shuts off after 5 seconds still. Engine light comes on. Acting like a security feature. Attached my scannner, an innova scanner & says "can not establish protocal"...... What next is it the ecm or a fuse or relay somewhere????? Lost in space here!!!!

 

Check all of your fuses. It is possible one blew from the voltage spike.