Method (METH) for measuring a distance R separating a vehicle and an identifier for accessing and starting the vehicle, the vehicle and the identifier being synchronized, the method (METH) comprising: - selecting (Sel_f p) N frequencies f p, p∈[1; N], N being a natural number at least greater than 3, between a minimum frequency f min and a maximum frequency f max, said frequencies f p being selected from among a plurality of frequencies F j, j∈[1;K], K being a natural number at least greater than 3, that are not situated at the centre of a plurality of predetermined communication channels (C bl, C wf); - implementing N sequences Sq p, each sequence Sq p comprising the following steps: • transmission (Em_S vp), from a transmitter (TXv) of the vehicle to a receiver (Rxi) of the identifier, of a first signal (S vp) of frequency f p • measurement (Mes_φ vip), by a computer (Xi) of the identifier, of a phase φ vip, modulo 2n, of the received first signal (S vp), in relation to a second signal (S ip) of phase φ ip (t) = φ 0ip + 2πf p t • transmission (Em_S ip), from a transmitter (TXi) of the identifier to a receiver (RXv) of the vehicle, of the second signal (S ip), said second signal (S ip) being generated by a phase-locked loop (PLLi) of the identifier I, such that its phase has the value φ 0ip and its frequency has the value f p • transmission, to the receiver (RXv) of the vehicle V, of the phase φ vip that it measured beforehand • calculation (Mes_ φ ivp), by a computer (Xv) of the vehicle, of a phase φ ivp, modulo 2n, of the received second signal (S ip), in relation to the first signal (S vp) • calculation (Cal_φ p), by a computer (Xv) of the vehicle, of the average φ p of the phase φ vip and of the phase φ ivp - for each value of p between 1 and N-1, calculation (Cal_P p), by a computer (Xv) of the vehicle, of a gradient P p using the formula P p = (φ p+1 -φ p)/(f p+1 -f p) - calculation (Cal_R), by a computer (Xv) of the vehicle, of the distance R on the basis of the gradients P p, pe[1;N]. - selecting (Sel_f p) N frequencies f p, p∈[1; N], N being a natural number at least greater than 3, between a minimum frequency f min and a maximum frequency f max, said frequencies f p being selected from among a plurality of frequencies F j, j∈[1;K], K being a natural number at least greater than 3, that are not situated at the centre of a plurality of predetermined communication channels (C bl, C wf); - implementing N sequences Sq p, each sequence Sq p comprising the following steps: • transmission (Em_S vp), from a transmitter (TXv) of the vehicle to a receiver (Rxi) of the identifier, of a first signal (S vp) of frequency f p • measurement (Mes_φ vip), by a computer (Xi) of the identifier, of a phase φ vip, modulo 2n, of the received first signal (S vp), in relation to a second signal (S ip) of phase φ ip (t) = φ 0ip + 2πf p t • transmission (Em_S ip), from a transmitter (TXi) of the identifier to a receiver (RXv) of the vehicle, of the second signal (S ip), said second signal (S ip) being generated by a phase-locked loop (PLLi) of the identifier I, such that its phase has the value φ 0ip and its frequency has the value f p • transmission, to the receiver (RXv) of the vehicle V, of the phase φ vip that it measured beforehand • calculation (Mes_ φ ivp), by a computer (Xv) of the vehicle, of a phase φ ivp, modulo 2n, of the received second signal (S ip), in relation to the first signal (S vp) • calculation (Cal_φ p), by a computer (Xv) of the vehicle, of the average φ p of the phase φ vip and of the phase φ ivp • transmission (Em_S vp), from a transmitter (TXv) of the vehicle to a receiver (Rxi) of the identifier, of a first signal (S vp) of frequency f p • measurement (Mes_φ vip), by a computer (Xi) of the identifier, of a phase φ vip, modulo 2n, of the received first signal (S vp), in relation to a second signal (S ip) of phase φ ip (t) = φ 0ip + 2πf p t • transmission (Em_S ip), from a transmitter (TXi) of the identifier to a receiver (RXv) of the vehicle, of the second signal (S ip), said second signal (S ip) being generated by a phase-locked loop (PLLi) of the identifier I, such that its phase has the value φ 0ip and its frequency has the value f p • transmission, to the receiver (RXv) of the vehicle V, of the phase φ vip that it measured beforehand • calculation (Mes_ φ ivp), by a computer (Xv) of the vehicle, of a phase φ ivp, modulo 2n, of the received second signal (S ip), in relation to the first signal (S vp) • calculation (Cal_φ p), by a computer (Xv) of the vehicle, of the average φ p of the phase φ vip and of the phase φ ivp - for each value of p between 1 and N-1, calculation (Cal_P p), by a computer (Xv) of the vehicle, of a gradient P p using the formula P p = (φ p+1 -φ p)/(f p+1 -f p) - calculation (Cal_R), by a computer (Xv) of the vehicle, of the distance R on the basis of the gradients P p, pe[1;N].