AFA41.8T

I have a 2000 Audi A4 1.8T that i made a big mistake recently and had the jumper cables hooked up backwards while trying to jump start the car. Now when i try to start the car it cranks but will not start. There are no check engine lights or ecs lights when i first turn the key on. I know the fuse to the radio is gone and the alternator is probablly gone too. I tried another engine computer and that still did not fix the problem. Did i fry a wire to the ecu or battery? Everything turns on in the car except the radio and the engine computer. The starter works and the fuel pump is coming on. I just want to find out what wire i may have fried and replace it.

Thanks for your help

4Driver4

Jump starting a car should be an absolute last resort. The "donor" car should never be running.

You probably damaged a fusable link. Get a wiring diagram and start looking.

AFA41.8T

I have tested all the relays, the fuel pump relay stopped working but even with forcing that to work the ecu will still not come on. I have a used ecu that i put in there and its not starting as well. what signal or signals make the ecu come on? I have a bentleys manual and everything according to their wiring diagrams seems to pan out. but the ecu is still not coming on.

Pete@ECSTuning

If you turn the key to on but don't start, what comes on? Do you hear the fuel pump prime?

AFturboA4

The fuel pumps primed and all the electronics come on inside the car, the battery light comes on also. The ECS light and check engine light do not come on though. I have recently sent my ECU to APR to get checked out and they said it checked good.

Pete@ECSTuning

Have you scanned it for codes?

FishMan

Don't rule out your ignition switch. I just went through a no strart issue and thought my coolant temp. sensor was to blame, which it could have been, but I'm having the same problem and noticed that when I turn the key and my dash lights up it starts and when it doesn't it won't start. This will be the fourth time I've replaced the ignition switch.

AFturboA4

I can't read any codes because when i hook up to it it says there is an error connecting to the computer. I am pretty sure the computer is not turning on at all. Now i have to look at the wiring to see what i fried. Any ideas on places to start?

4Driver4

Is your CEL working when you turn the key to the on position?
Is your ABS light on?
Do you have an aftermarket radio?

AFturboA4

No i dont have a CEL on when turning the key on, i do have the ABS light and it still has the stock radio in it.