Have an audi a4 1.8T Cabrio. Battery went dead,

double posted, why?
JUMPS OK
AFTER JUMP WORKS AND DRIVING, AND STOP AND KEY OFF
IT WILL NOT CRANK.
did i guess right?
that means ,
check all fuses first. even the alt fuse (large)
1-battery bad? #1 top failure all cars.
2-Charge system bad. (is the charge/ batt warn lamp glowing when running car, bingo.????

3-or phantom drains. (if no crank just after stall then it not this) if drains while sleeping yes.

the tests are easy, a dirt cheap voltmeter
13.3v to 15v running is good charge system.
if 12v and falling not.

if the battery is bad, the charge system can shut down, so, the best practice is to try a know
good battery out of 2nd car, do you have battery to barrow, this is TOP CHOICE< not thinner wallet.

if the good battery fails then the charge system is failing (note I said system and not a part)
or the belt missing or slipping to the alternator.

btw the 4.3L PCM runs the alternator
PCM is engine brain.
btww, same true 2.2l engine.
the regulator is in the PCM.

so is the charge/bat lamp in cluster
on key on, lamp test
the jump start it , it runs
does the charge./batt.lamp go out.
id be all over that lamp, costs nothing to look.

Try it & see

It is the anti theft device that sends the alarm off and changing the battery sets of the circuit in the CPU . Use a code reader to reset the CPU

check your battery cables for corrosion clean them and start the engine

Dead Battery --Replace it

Sounds like your security system thinks your stealing it. Try locking and unlocking manually. Jump starting can sometimes damage electronics not usually a good idea. It is better to disconnect the battery and charge it then reconnect it. You may have blown the EBS fuse which may be mounted ont the ebs computer.

You will need to enter the anti theft radio lock code. I would check the manual for the operation. On my VW it was on a sticker in the truck. Also check with an Audi dealer for exact location.

you have spiked the computer, you did not correctly jump the battery in the correct manner, you jump the batterry by hooking up the leads from the donor car to the problem car remembering not to conect the negative to the batterry but only to the body of the car, and still you do not crank the car whiel jumping, you wiat 5 mins unhook the jumpers then start, if this does not work you have a faulty batterry. nwo to fix your problem you must by a newcomputer or see a specialised auto techinician who might be able to save you some money.

You need to Check out the Alternator.