These cars suffer from one problem and that is the computer ,as the O2 sensor heaters run the earth back through a transistor switch in the ECU ,so what i do is run a seperate earth from O2 sensor heater side to chassis or engine this cures the fault so vehicles passes the emmisions but the engine light will stay on .on the O2 sensor are two white wires these are the heater wires ,one will read a positive but no earth continuety ,run a earth and it will work .