hi, im new here. cutting a long story short, i have a 2003 bmw 318 ci sport. 2L, had the car for over a year, then started firing codes at me. used the peake tool recoved code table 21 fault 271D "Oxygen Sensor heater before cat". according to RealOEM below there are 5 Oxygen sensors. how do i determine which one i need to change, as its only came up with "Oxygen Sensor heater before cat"
any help would be appreciated,