Bosch Mass Air Flow sensor
VW uses several Bosch MAFs for its TDIs. Bosch number 0 281 002 216, VW number 028 906 461 and also Bosch number 0 280 217 121, VW number 06A 906 461. As far as I know these MAFs are equal. The drawn transfer curve drawn is from a Bosch 0 280 218 018 MAF. I'm pretty sure this curve is equal to the curve of the previous mentioned MAFs. The wire colors and the connections mentioned to the ECU are from a 66kW ALH engine.
A Bosch MAF has 5 pins:
Temperature sensor output, not used in ALH engine
12V supply input
Connected to -