Cam-HALL inverter - (standard since 2008-06 on motronic55 boxes unless requested othewise) - subpage of InputTrigger/AudiTrigger

The default is good, and only effects "ignition outputs" and "trigger tooth" (to make 360 crankdegrees difference). Everything below is only for the very curious power-users

Cam-HALL signal is used to mask one of the 2 crankhome pulses.

It has little significance normally. But with the special 7A flywheel that has 2 notches, the HALL signal polarity gets important. VEMS listens when the processor sees a 5V signal, and neglects any crankhome-VR pulses when the processor sees 0V signal. With the more usual "mostly 5V" HALL sensor the cam-HALL inverter is installed between the input pin and the processor: it helps filter out the VR noise from the 7A flywheel (and other noise too).

As MembersPage/DesmondAudi shows, at least some of the AAN engines are equipped with "mostly 0V" HALL sensors. In such cases the ECU should NOT have the cam-HALL inverter.

"mostly 5V" HALL sensor: (cam-HALL inverter is good !)

"mostly 0V" HALL sensor: (cam-HALL inverter actually makes it more noise-prone !)

For [Audi 7A flywheel] that has some notches that disturb the crankhome-VR signal, an inverter is needed to neglect the big window around 134deg BTDC cyl5 (and keep the small window around 62 BTDC cyl1).

The inverter can be an NPN transistor such as TIP31 or BC817 (almost any NPN transistor that can handle 10mA and 20V)

Cam-HALL inverter is essential for 7A flywheel, and recommended for all InputTrigger/AudiTrigger installs. Mention the audi engine-harness type AAN/ADU/ABY or 3B or 7A in the order note.

Operation with failed cam-HALL sensor ("limp-home")

The factory audi cam-HALL sensor is known to break relatively often, especially old (original) sensor in an overheated engine bay, especially the sensor in the distributer (the sensor at the front, as in some engines, seem to fail less often). We've seen small unipolar HALL-sensor [SS443A] hacked into the distributer but we don't know how difficult it is to apply it reliably.

The motronic cannot start with a failed HALL sensor. VEMS can start with failed HALL sensor, appr. 50% of the time (need to crank a few more time if backfires), if:

Verifying if my controller has camHALL inverter or not


But you can easily verify: