A method for diagnosing an inversion of a crankshaft sensor includes the following steps: acquiring a signal by way of the crankshaft sensor, at each detection of a tooth, determining a tooth time elapsed since the previous tooth detection, at each detection of a tooth, calculating a ratio Ri of the tooth times according to the formula Ri=(Ti−1)2/(Ti*Ti−2), where Ri is the ratio, Ti is the last tooth time, Ti−1 is the penultimate tooth time, and Ti−2 is the tooth time preceding the penultimate tooth time, comparing the ratio Ri with a low threshold Sb, indicative of a turn marker, and a high threshold Sh, indicative of an absence of inversion, a ratio Ri between the two thresholds Sb, Sh being indicative of an inversion.