Engine 16 reponded along with E-11 and Rescue 18 to the intersection of Main Street and Olivia Street for the possible tractor trailer fire.  FD 1 arrived and advised that it was a working fire in the undercarriage of the trailer.  Members went to work using a preconnect off of E -16 and quicly had the fire under control.  Fire was apparently caused by equipment malfunction. The trailer was hauling cooking oil.