Case study: 01986 - Convertible Top Frame Position Sensor (G356)

[NEtech]

Audi A4 Cabrio 2008
Periodic Convertible Top could not close.

G365 changed.

 

[DV52]

NETech: very interesting - I probably should know the answer, but what are the scales in the graph? Sorry, but graphs without axis descriptors is a pet-peeve of mine!!

Don

 

[Uwe]

NETech: very interesting - I probably should know the answer, but what are the scales in the graph? Sorry, but graphs without axis descriptors is a pet-peeve of mine!!

I believe MVB 001.4 in that 0x26 module is a field that lacks units; it's just a value with a range of 0 to 255.

-Uwe-

 

[NEtech]

Yes potentiometer (G365) raw values.

1 kOhm

 

[Jef]

Thank you, indexed.

 

[Uwe]

Yes potentiometer (G365) raw values.

Those kinds of position sensors are designed in such a way that the raw value never goes to the extreme end of the range (in this case, 0 or 255), and if it does, the control module interprets that as a malfunction.

-Uwe-

 

[DV52]

^^^^^^^hmm...... OK, so notwithstanding that NETech's picture shows a variable 1Kohm resistor, the chart (module?) quantizes the readings from pot's slider into 255 x positions along the roof's travel. I assume this is what Jeff means by "indexed". Makes sense - but what then causes the lag in the new sensor's trace? Isn't the horizontal scale time and if so, just changing the sensor shouldn't alter the time response of the roof from the starting position?

Don

 

[NEtech]

This is just 2 different open/close runs, one good and one bad.
I have defined the x-scale start and stop, I made a offset so it is easier to see.

 

[Jef]

Indexed, as in I added this thread to the super sticky index.
https://forums.ross-tech.com/showthread.php?18464

 

[Ronaldo]

Those kinds of position sensors are designed in such a way that the raw value never goes to the extreme end of the range (in this case, 0 or 255), and if it does, the control module interprets that as a malfunction.

-Uwe-

Interesting. I suppose the potentiometer is connected to a VCC and the voltage on the cursor is read by an analogue-to-digital converter (one byte, values 0 to 255) with limits defined by the controller module. But if there is some dust on the potentiometer's resistive track it can make the cursor to lose contact with the track, then the voltage on the cursor can go momentarily to zero, even though it's a value out of range. Am I correct?

 

[Uwe]

Am I correct?

Yep. Also a broken or shorted wire will be picked up as an out-of-range condition.

That said, for really critical applications like the accelerator pedal position sensor and the throttle position sensor, they use two potentiometers on the same shaft and cross-check the values in addition to making sure they're not out of range.

-Uwe-

 

[NEtech]

In this case the low and high value are learned and saved in the controller.
If G365 or the controller is exchanged, you have to run adaptation, Channel 01.
And run a full open and close sequence, to learn lowest an highest value.