Use the following information as an aide when testing BMW E39 dual MAF sensors. Keep in mind, a problem with mechanical engine components can affect MAF readings and besure you have a solid base engine before condeming parts.

KOEO (Key On – Engine OFF)taken at sensor back probing with DVOM
B1 AFM 1.02 Volts
B2 AFM 1.02 Volts
Using scan toolBoth AFM sensors read 0.9 Volt on GT1 under maf data stream.

Hot, engine running at idle taken at sensor back probing with DVOM
B1 AFM 1.30 Volts
B2 AFM 1.29 Volts
Using scan toolBoth AFM sensors read 1.0 Volt on GT1 under maf data stream.

2500 RPM taken at sensor back probing with DVOM
B1 AFM 1.85 Volts
B2 AFM 1.75 Volts
Using scan toolBoth AFM sensors read 1.5 Volt on GT1 under AFM data stream

IAT sensor not used on bank 2 AFM. However sensors are interchangeable.

Testing using a labscope. In Park or
Neutral, parking brake on.
Snap throttle to reach max voltage output.
(scope pattern shows a dual trace of both
AFM’s.

The sensors should be within 0.1 volts of each other.