What was found
IMMEDIATELY AFTER TAKEOFF, THE RED SMOKE AFT LAV WARNING DISPLAYED. THE FA CALLED AND REPORTED THAT THE SMOKE DETECTOR WAS GOING OFF, AND THAT THERE WAS A STRONG ODOR IN THE CABIN. PER THE NON-NORMAL CHECKLIST, THE LAV EXHAUST FAN O/B WAS PULLED. THE WARNING WENT OUT. FOUND SMELL TO BE FROM LAV EXHAUST FAN. DEFERRED LAV EXHAUST FAN IAW PER MEL 21-23-2. PLACARD INSTALLED. C/B PULLED AND COLLARED. MXC NOTIFIED. TRANSFERRED TO MMO2. REMOVED AND REPLACED AFT LAV FAN IAW CRJ900 AMM 21-23-93 PN GG670-95028-3 SN OFF 01071 SN ON 01206. ALL CHECKS GOOD.