W T E C I I I E L E C T R O N I C C O N T R O L S T R O U B L E S H O O T I N G M A N U A L
Main code 51 indicates a failed offgoing ratio test. An offgoing ratio test occurs during a shift and uses turbine and
output speed sensor readings to calculate the ratio between them. The calculated speed sensor ratio is then compared
to the programmed speed sensor ratio of the commanded range. After a shift is commanded, the ECU, after a period
of time, expects the old ratio to be gone. If the ratio does not change properly, the ECU assumes the offgoing clutch
did not release. The shift is retried if conditions still exist to schedule the shift. If the second shift is not successfully
completed, code 51 XX is set and the ECU returns the transmission to the previous range. Additional codes could be
logged for other shifts where X indicates the range from and Y indicates the range to.
This test is not performed below a calibrated transmission output speed of 200 rpm.
Active Indicator Clearing Procedure:
Manual except subcodes 35, 42, 43, 45, 53
Before troubleshooting, read Paragraph 56. Also, check battery and ECU input voltages.
Intermittent connections or lack of battery-direct power and ground connections may cause this and
1. Incorrect fluid level can cause 51 series codes. Allow the vehicle to idle for 34 minutes and check
the transmission fluid level. If level is not correct, add or drain fluid to correct level.
2. If the fluid level is correct, connect a pressure gauge into the pressure tap for the offgoing clutch
indicated by the code (refer to solenoid and clutch chart, Appendix C). Make the shift indicated by
the subcode or use the Pro-Link® diagnostic tool clutch test mode to put the transmission in the
off-going and oncoming ranges (refer to Appendix B for clutch pressure check information).
XY upshift or downshift
CODE 51 XX OFFGOING RATIO TEST DURING SHIFT (TIE-UP TEST)