Having problems with CEL code 43. Able to fix problem by replacing O2 sensor, however after 3 to 4 weeks the CEL code 43 returns. I have a new CAT, fuel pump, fuel filter, O2 sensor. No problems with fuel injector, no short in electrical system. Not having any performance issues. Thinking maybe ECU needs to be replaced. Any suggestions ????

 

maybe your gas cap or a vacuum leak... do some googling in this forum