1. A 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, said sensors being fixed relative to said stator, and able to detect a magnetic field and provide first signals which are representative of said magnetic field, said method comprising the steps of: generating, from linear combinations of 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 said rotor; determining a first parameter known as a speed state E vt of said 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 said first sinusoidal signal ( 200 ), C pp is the maximum peak-to-peak amplitude and C is the instantaneous value of said second sinusoidal signal ( 201 ), and TRIG_PP, V ref and Δ are three predetermined threshold values; determining, when said speed state parameter E vt is greater than zero, the logic state “TRUE” or “FALSE” of said first equation, and generating a signal ( 400 ) which indicates fault-free functioning of said sensors when said first equation is not confirmed, and a functioning fault of at least one of these sensors when said first equation is confirmed; and determining, when said speed state parameter E vt is equal to or greater than zero, the logic state “TRUE” or “FALSE” of said second equation, and generating a signal ( 400 ) which indicates fault-free functioning of said sensors when said second equation is not confirmed, and a functioning fault of at least one of said sensors when said second equation is confirmed.