What is the reason why the Audi A6 tachometer sometimes works and sometimes doesn't?

[LeZoey]

Audi A6 tachometer sometimes works and sometimes doesn't, the reasons are: Poor combustion state: Poor engine combustion state is the main reason for the engine fault light to come on. Engine knocking: Engine knocking usually has three situations: The first situation: The car lacks power; The second situation: The car lacks power, and the engine noise is too loud; The third situation: There is an obvious knocking sound from the cylinder. In the first situation, some engine fault lights will come on, some will not, in the second and third situations, the engine fault light will inevitably come on. Reasons for the engine fault light to come on: Poor fuel quality; The inside of the engine cylinder is not clean, with accumulated carbon deposits.