Method for determining a function state (FZ) of an ultrasonic sensor (2) for a vehicle (1), having the steps of: a) applying (S1) an electrical test signal (P) to the ultrasonic sensor (2); b) detecting (S2) an electrical response signal (A) from the ultrasonic sensor (2); c) determining (S3) a phase-frequency response (PF) comprising the phase angle (a) of the detected response signal (A) for the applied test signal (P) on the basis of an excitation frequency (f) of the applied test signal (P); d) comparing (S4) at least a first phase angle (P1) below and a second phase angle (P2) above a resonant frequency (R) in the determined phase-frequency response (PF) with a respective expected phase angle (PE1, PE2); e) correcting (S5) the determined phase-frequency response (PF) on the basis of the comparison; and f) determining (S6) the function state (FZ) on the basis of the corrected phase-frequency response (PFK).