6–98 Copyright © 1998 General Motors Corp.
WTEC II ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
Main code 56 indicates a failed range verification speed sensor ratio test. The ratio test occurs after a shift and
determines if a clutch has lost torque carrying capability. If output speed is above programmed output speed for a
range but the correct speed sensor ratio is not present, the DO NOT SHIFT response is commanded and a range
which can carry the torque without damage is commanded or attempted. Turbine and output speed sensor readings
are used to calculate the actual ratio that is compared to the commanded ratio. Main code 56 can also be caused
by the EEPROM being calibrated for a close ratio transmission and installed in a wide ratio transmission, or
vice versa.
Active Indicator Clearing Procedure:
• Power down
• Manual — subcodes 11, 44, 66, 77 only
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.
NOTE: Energizing the solenoids and listening for ball/plunger movement is sometimes useful in
troubleshooting.
Troubleshooting:
1. After the transmission is at operating temperature, allow vehicle to idle on level ground for 3–4
minutes. Check the transmission fluid level. If improper fluid level is found, correct as necessary.
Improper fluid level could be the cause of the code. Not enough or too much fluid may produce
inadequate clutch pressure.
2. Connect a pressure gauge and check main pressure. If the pressure is not adequate, the pump is
probably worn. See Appendix B for main pressure specifications.
3. If main pressure is adequate, check clutch pressure for the range indicated by following the
procedure in Appendix B. The transmission range indicated by the trouble code can be found by
referring to the solenoid and clutch chart in Appendix C. Drive the vehicle or use the diagnostic
tool’s clutch test mode and check clutch pressure.
Main
Code
Subcode Meaning
56 00 Range verification ratio test (between shifts) L
56 11 Range verification ratio test (between shifts) 1
56 22 Range verification ratio test (between shifts) 2
56 33 Range verification ratio test (between shifts) 3
56 44 Range verification ratio test (between shifts) 4
56 55 Range verification ratio test (between shifts) 5
56 66 Range verification ratio test (between shifts) 6
56 77 Range verification ratio test (between shifts) R
CODE 56 XX — RANGE VERIFICATION RATIO TEST (BETWEEN SHIFTS)
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