[RahX]

which engine? if its the 3.8 with the crazy plastic intake, they have a problem with the o-rings on the upper plenum leaking because they get hard. this would set a lean code, 171. the 153 MIGHT be due to the lean condition. the 154 does not show up on the code list so i dont know what to tell ya there. also the 3.8s have problems with head gaskets. the coolant leaking into the cylinders may not be doing anything noticeable now but they can take out an O2 sensor pretty quick. your mechanic should be able to see coolant on the o2 so that may not be the case.