Advice wanted: P0171 only Motorways

[olurkio]

E110 often reacts to being on a motorway with a engine warning light.

It never comes on when country or urban driving so I think it must be something to do with the fuel system. My reasoning is that a vacuum leak would be present at all times. 

Has anyone else experienced this, I'd love to get to the bottom of this issue?

(2000 E110 Sportlift back, 1.6 VVTi auto 95K on the odo) 

[oldcodger]

Hi,

There are several possible causes of that error code,  if you search the web you will find lots of pages and ytubes detailing that error and identifying the root cause.

Could be as simple as correctly and carefully cleaning the MAF sensor as mentioned here  -

https://www.way.com/blog/how-to-fix-a-p0171-code/#Common_errors_in_P0171_code_diagnosis

[flash22]

It's a lean code as it only happens at higher speed i would say it's fuel related (higher the speed the more fuel the engine requires) given the age and mileage it's likely the fuel filter sock on the pump is clogged or the pump itself is at the end of its life

[oldcodger]

If its as @flash suggests, might be worth checking the fuel filler pipe, seem to remember reading about earlier ones were made of metal and corroded which could be the source of any blockage,  assume your fuel tank is plastic like our 2006 model.