S40 (New) Engine 2.4 : DTC P0171 diagnostics over OBD2 (O sensors?)

[NikOmatic]

Hey all!

I've been diagnosing P0171 (lean bank 1) after it failed my s40 in tech. inspection (emissions testing passed, but inspection failed purely because OBD is giving out P0171 DTC). I'm trying to narrow down the cause by looking at OBD data before I start spending money on parts.


What confuses me the most is the O2 sensor data - it is not at all similar to what near all online resources suggest O2 data should be.

OBD data reports two oxygen sensors:
O2S11(mA) (upstream?) - stays around +/-0mA on idle or constant RPM, jumps up to +1.5mA increasing RPM.
O2S12(V) (downstream?) - stays around 0V on idle, jumps up to +0.8V with increasing RPM, and levels out to +0.6V with constant RPM in 2K range.

Near all the information online says that O2 sensors output 0 to 1V, upstream sensor oscillates, and downstream sensor should be static around 0.5V. No mention of current output sensors anywhere.


FP (fuel rail pressure?) is around 370kPa which seems fine based on generic info I've looked up, so fuel pump and filters are fine.



MAF is around 2.5g/s and does go up when accelerating (no idea if these are OK looking values). I did the test of unplugging MAF and seeing if the car stalls - it barely stumbles and continues running normally, which is supposed to indicate bad MAF. This MAF unplugging test seems like a completely dubious way of testing anything though, so I am hesitant to buy a new MAF based on just that.



If those MAF and O2 reading are fine, then I will have to look for vacuum leaks again. No other ideas really.