Hi all, our 2015 D4 has started showing the above message recently.
on diagnosis it seemed to indicate issues with MAF so that has been replaced but now showing low air flow or something.
air filter replaced and complete intake system cleaned.
aux battery has been replaced as I believe this can throw up random messages if battery is knackered
Car is driving fine but occasionally idles roughly and misses that top end punch when overtaking so definitely down a little bit on power.
Any suggestions before I take it to a main stealer to get raped?
thanks in advance.

 

If it's VEA engine - check EGR and EGR cooler.
BR

 

ok thanks. Check for damage? Blockage?

 

Blockage. On VEA engines, EGR cooler gets blocked, lowering air flow to the engine. That's why MAF errors where (wrongly) reported, and issue is not solved by replacing it.
VEA engines are known for very bad EGR cooler design, where air flow makes 180 degrees turn.
BR

 

managed to check EGR valve movement and arm is moving freely but I guess this is no indication of state of cooler and no way of checking that without removing and splitting unit.
Currently in Spain (with car) for a few months so no chance of doing it myself.