Hello Robs,
Unfortunately, I can't tell you what a TP sensor is. If it stands for "Throttle Position," then it's the throttle position sensor, which is essentially the accelerator pedal potentiometer. Based on my information, diesel engines with fully electronic control systems always have a throttle position sensor. There's no longer a throttle cable connected directly to the fuel injection pump (especially not with common rail systems).
Das Gaspoti is responsible for transmitting your gas commands to the EDC, so it provides the STG with information about the pressure you are applying with your right foot

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