2002 Mercury Villager/pain in the rump!

This van has a little under 100000 miles on it, but it has been a headache since we bought it in 2005. It recently caught fire underneath. It was found that our valve cover gasket wore don and oil poured onto the cat and caught fire. whenever we took it to the shop to get the damage assessed, we had them check the check engine light that had been on forever. It had a couple of codes, an 02 sensor (bank 1, sensor 1), and a knock sensor code. when they had everything dismantled, i had them go ahead and replace the o2, and the knock. Recently, the check engine light has come on again and now it is reading; o2 sensor heater circuit malfunction (bank 1 sensor 2), knock sensor 1 circuit malfunction (bank 1 or single sensor) and camshaft position sensor circuit malfunction…i was wondering if the fire could have burned part of the wiring harness…any ideas?! please help!!!