1. Method for diagnosis of functioning faults which exist in sensors implemented in a system for measurement of the angular position of a rotor of a polyphase rotary electrical machine comprising a stator, the sensors being fixed relative to the stator, and able to detect a magnetic field and provide first signals which are representative of this magnetic field, characterised in that it comprises at least one step of generating from linear combinations of the said first signals ( 101 - 103 ), at least one pair of first ( 200 ) and second ( 201 ) sinusoidal signals, which are dephased by a predetermined value different from zero and from 180°, representing an angular position of the rotor; determining a first parameter known as the speed state E vt of the rotor, which assumes two values E vt >0 or E vt ≧0, calculating the following first and second equations: 
 −[( S pp <TRIG — PP ) OR ( C pp <TRIG — PP )]; 
 −[( V ref −Δ<S<V ref +Δ) AND [( V ref −Δ<C<V ref +Δ)], in which “OR” is the non-exclusive disjunction logic operator and “AND” is the conjunction logic operator, S pp is the maximum peak-to-peak amplitude and S is the instantaneous value of the said first sinusoidal signal ( 200 ). C pp is the maximum peak-to-peak amplitude and C is the instantaneous value of the said second sinusoidal signal ( 201 ), and TRIG_PP, V ref and Δ are three predetermined threshold values; determining, when the said speed parameter E vt is greater than zero, of the logic state “TRUE” or “FALSE” of said first equation, and generating a signal ( 400 ) which indicates fault-free functioning of the said sensors when this first equation is not confirmed, and a functioning fault of at least one of these sensors when it is confirmed; and determining when the said speed state parameter E vt is equal to, or greater than zero, the logic state “TRUE” or “FALSE” of the said second equation, and generating a signal ( 400 ) which indicates fault-free functioning of the said sensors when this second equation is not confirmed, and a functioning fault of at least one of these sensors when it is confirmed.