I have been advised that bank 1 sensor 1 is lean and the O2 sensor faulty. Replaced it and no change. The scan tool is not even picking up Bank 1 sensor 1 but is picking up the downstream sensor. What could be the cause and how do i repair the problem. The vehicle is underpowered especially on inclines and when hot whilst driving and seems to be ok at idle. Check engine light comes on and fault code is p0171. Vehicle is a C180 Kompressor 2006 W203 with M271 engine. Engine rebuilt and has done 11000kms....power fault noticed in first 1000kms was intermiitant then went away and now has in the last 2000kms got progressively worse.
Why would the scan tool not pick up bank 1 sensor 1?