The ABS pump is NOT supposed to run every time you switch on the ignition. It should only run when:
- driving, and the ABS ECU detects a condition that requires additional hydraulic fluid pressure.
- testing, for example activating the pump actuator with FiatEcuScan.
If it does turn on when the ignition is switched on, this is an indication that there is a problem in the ABS control module. If left uncorrected, this will result in an expensive repair, as the pump unit will soon wear out, and will have to be replaced.
My guess is that about 90% of ABS control module problems are caused by (total or partially) failed transistors/diodes. These are easily damaged by static electricity and power spikes that may occur, such as:
- jump-starting (to or from) another car.
- careless connection of the battery terminal, causing sparks, instead of making a solid once-off connection (the negative terminal should be connected last for safety reasons).
- careless electric arc-welding on the car, see this thread:
Fortunately, if you are handy with a soldering iron, this is an inexpensive DIY repair. I recommend that you first replace the three transistors and one rectifier bolted onto the two heat-sinks in the controller unit, and see how it goes. If you are bad luck, and have a damaged ABS ECU, your only other option would be to replace the whole ABS controller unit, since the ECU is much more difficult to repair.
The same Bosch ABS 5.7 system is also used in some BMW models. The guys on the BMW forum have done some excellent work on diagnosing and repairing ABS related problems. Some of them have even managed to repair their ECU's. For more information, see this thread:
HELP! ASC ABS Problem E39 523i - Bimmerforums - The Ultimate BMW Forum