6–88 Copyright © 1998 General Motors Corp.
WTEC II ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
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.
NOTE: This test is not performed below a calibrated transmission output speed of 200 rpm.
Active Indicator Clearing Procedure:
• Power down
• Manual — except subcodes 35, 42, 43, 45, 53
NOTE: Before troubleshooting, read Pages 6–17 and 6–18 of Section 6–5. Also, check battery and ECU input
voltages.
NOTE: Intermittent connections or lack of battery-direct power and ground connections may cause this and
other codes.
Main Code Subcode Meaning
51 01 Low–1 upshift
51 10 1–Low downshift
51 12 1–2 upshift
51 21 2–1 downshift
51 23 2–3 upshift
51 24 2–4 upshift
51 35 3–5 upshift
51 42 4–2 downshift
51 43 4–3 downshift
51 45 4–5 upshift
51 46 4–6 upshift
51 53 5–3 downshift
51 64 6–4 downshift
51 65 6–5 downshift
51 XY X to Y shift
CODE 51 XX — OFFGOING RATIO TEST DURING SHIFT (TIE-UP TEST)
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