Allison WTEC II Fault Code: 54 PID: SPN: 01 FMI: Oncoming ratio test (after shift), L to 1

Main code 54 indicates a failed oncoming ratio test. L?1 upshift

The ratio test after a shift is failed when the ECU has commanded the end of a shift and has not seen the transmission shift into the target range (comparing turbine and output speeds). Erratic readings from speed sensors are a likely cause of an oncoming ratio test failure. If conditions for a shift still exist, the shift will be retried one more time. If the ratio test is still not met, a code is logged and the DO NOT SHIFT response is commanded. If the code is set during a direction change, Neutral with No Clutches is commanded, otherwise the transmission is commanded to the previous range.