328i O2 sensor wierd error issue

[slyder]

Hi taiko'swould need some feedback and help in having to correctly find the root cause of this error.055 output stage, Oxygen Sensor heater, Sensor1, Cylinder 1-3 before cat1) There are 2 328i e36 which have both replace the 2 o2 sensor. 2) Both still shows this error even after doing a swapping the o2 sensors socket between sensor 1 and sensor 23) fc for the cars have improve slightly but still not reaching 400km per full tank.4) no idling or erratic engine behaviour on both cars.Main confusion is because according to the specs listed online, e36 328i should have 4 sensors but on our ckd only 2 were found.where the other 2 sensors sockets are supposed to be locate next to the fuel filter there is nothing there.apparently our 328i were assembled in sabah according to a friend.Any advice on how to proceed on this?Cheers