Testing turbo VNT actuator position sensor?

[yason]

After some VNT trouble last year I have the turbo off my DS5 hdi163 (RHH) on the bench for cleaning the VNT vanes. While I'm at it I'd like to test the VNT actuator position sensor as well but it seems I don't seem to get anything sensible out of the three pins.

Does anyone know how to test the position sensor that sits on top of the actuator? I assume it has a potentiometer or hall effect position sensor inside but I wonder if the three pins correspond to those directly? Or if there's something else that's required? My understanding is that given a reference voltage the signal voltage will then vary depending on the rod position.

I've seen P2563 which is turbo VNT position difference between copied and requested. This is fine if it was the vanes that got stuck for a while but it's also possible the position reading was bad. The position reading is what I'd like to test now that I have access.

Sedre gives me the following details for the wires:

• 1419A: sensor supply
  1420A: sensor earth
  1421A: sensor signal

Using a bench power supply and an oscilloscope I fed +5V to supply, connected earth to earth and set up my scope between the signal wire and earth. I get a steady voltage of about 0.9V on the signal wire but that does not change when I supply vacuum to pull the actuator rod back and forth between the shortest and longest positions.

If the pins do correspond to the internal sensor component directly then I'd say the actuator sensor is shot. But I'm not sure of the correct test procedure and if anyone knows more about this, please share. I'd like to get some confirmation one way or another before I buy a new actuator unit.

[yason]

As a follow up, problem sorted:

The wiring was a bit trickier but once I found the correct order for earth/supply/signal at the connector I started getting readings that respond to the actuator rod position. There's a hall-effect based position sensor inside the actuator, giving a signal between 0-5V that tells the actuator rod position to the ECU. The old actuator gave me a signal voltage between 1.5-3.3 V which is a subset of the expected range. I bought a new actuator and that one reported 0.5-5.0V which I think is roughly correct.

I installed the new actuator and took a look at live data in Diagbox while driving. The measured turbo pressure was tracking the expected pressure very steadily, and the measured VNT actuator rod position similarly followed the expected position, even in full-throttle acceleration. That should let the car drive now without fault codes from turbo VNT position, hopefully.

So, the gist of it is that the position sensor can go bad. (Or be bad, from the factory.) The old actuator still operated perfectly under vacuum, retracting the rod as requested but the position signal just meant that the ECU saw erroneous signal at the very low and high end of the scale.

The new actuator is from NTY. Don't know about the manufacturer but at least they dared stamp their own name on the actuator so it can't be total trash.