Last week I got the single fault code of P0171 System Too Lean (Bank 1),
I was advised by BMW mechanic that 95% would be the MAF Sensor in Bank 1 was defective,
so i replaced the maf sensor with BOSCH part# 0280217110, install new air filters and cleared the codes.

After driving the car for 30+ miles the "Service Engine" light came on again and now the error codes are:

P0171 - System Too Lean (Bank 1)
P1270 - Control Module Self-Test, Torque Monitoring

can someone on the forum provide some troubleshooting tips on where to check to fix the error codes.

Thanks in advance for your help.