3 days ago i bought a 2004 STi.
The previous owner informed me that has changed 1 year ago in warranty the alternator and the battery.
From curiosity i measured today the Bat Voltage and realized that if there is no electrical consumption from the heater or lights or defog switch the BV is 12-12,3 Volts only, like the alternator is not charging.
If i turn on, one of the above devices the BV is 13,9-14,1 Volts (i find this right).

I checked the BV on 2 other cars, a 2003 WRX and a 2003 STi, and i saw that they have constant 14 Volts no matter the electrical consumption.

What can be wrong with the charging system on my STi?
The car has only a clifford alarm system installed.

Any ideas would be really helpful.

Christos

Imprezas use a 'smart' alternator which doesn't charge unless something is switched on. I don't think you have anything to worry about unless your car doesn't want to start.

As above, switch on the headlights and the charging circuit should leap into life.

I checked one more WRX04 and had the same charging "attitude" as mine.
But i made a step further.
I swapped my ECU (AH990) with the ECU from another STi 04 and what i realized is that with the new ECU my car had all the time 14Volts and the other Sti the previous charging attitude (charges only when a load is applied).

Any comments?

Christos