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Allison WTEC II Fault Code: 54 PID: SPN: 21 FMI: Oncoming ratio test (after shift), 2 to 1

Main code 54 indicates a failed oncoming ratio test. 2?1 downshift

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.

Main code 54 can also be caused by the EEPROM being calibrated for a close ratio transmission and installed in a wide ratio transmission, or vice versa. Additional codes could be logged for other shifts where ?X? indicates the range from and ?Y? indicates the range to (there have been occurrences of Code 54 87, N1?R, for example).

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