Sep 15, 2020 · P0731 Code: Gear 1 Incorrect Ratio. The Axle Ratio is stamped on a Gear Ratio Tag on the axle cover. When referring to the transmission, the gear ratio is the difference between input speed and output speed. Although, with some tuning, you can get the 545RFE to. FORD: 2011 F-250, F-350, F-450, F-550 This article supersedes TSB 11-3-23 to add. The P0731 code occurs when the PCM detects a discrepancy between the speeds of first gear's input RPM sensor and transmission output RPM sensor.