Tt600 Throttle Position Sensor

TT600 THROTTLE POSITION SENSOR
HI folks , have a fault code of p0122 on my tt600 engine . It looks as tho this may mean low power from the throttle position sensor. Have checked the powers & have 0.55 v without any throttle & 3.8v at full throttle. The the input volts is 5.6v . I am told it should be close to 5v on full throttle . All these are done without engine running .
Is this correct as the engine sounds very sweet when running .
The engine does not look like it has been adjusted from new .
Any help would be appreciated as I Am not a mechanic but I do know a reasonable amount .
Many thanks
Phil G