In my observation of (Titanium PowerBook G4 DVI 800 MHz, 2002 "Ivory" PowerBook3,4 A1001), both fans are controlled independently, each in one of three states:
off (0 V)
low (3 or 3,3 V)
high (5 V)
Do you have a voltmeter or multimeter? Remove bottom panel, turn it on, hang TiBook off table/counter edge or use as closed clam, and measure fan voltage. If voltage is 5 V, then I might suspect damage resulting in fan always at high speed. If voltage is 3 V (low speed), then I might suspect standard behaviour thermal strategy.
off (0 V)
low (3 or 3,3 V)
high (5 V)
Do you have a voltmeter or multimeter? Remove bottom panel, turn it on, hang TiBook off table/counter edge or use as closed clam, and measure fan voltage. If voltage is 5 V, then I might suspect damage resulting in fan always at high speed. If voltage is 3 V (low speed), then I might suspect standard behaviour thermal strategy.