Not sure if this is in the right place but ...

Can anyone explain to me how the K-Line works between the ECU and sensors?

Is it just a case of fluctuating the voltage according to values, or is it encoded data?

If it is just fluctuating voltage is it a single wire pulsing solution of a pair etc etc?

Many thanks

'k' line does not work between the ECU and sensors, it is (for VAG) purely a single wire line for serial communication between the various ECU's and a diagnostic scan tool.

The diagram I have gives the impression it was a k-line going between a sensor and the ECU.

Can I take it that the K line is a serially encoded data format then, and that I would need to know the message formats, and data encoding (eg 10/8) to write to it.

If it isn't a K line going to the sensor, what would it be just a simple voltage feedback?

The diagram I have gives the impression it was a k-line going between a sensor and the ECU.

Can I take it that the K line is a serially encoded data format then, and that I would need to know the message formats, and data encoding (eg 10/8) to write to it.?

Yes

If it isn't a K line going to the sensor, what would it be just a simple voltage feedback?

It may be, but other formats like PCM or variable freqency are used it depends which sensor you mean.

DPF pressure sensor (G450 on the superb)

This is the start of a long line of working things out