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Code 68, Overdrive Ratio Error: Notes

WARNING: This page does not describe the selected car, but rather 24 other vehicles, including the 1992 GMC Yukon, 1992 GMC Vandura Special, 1992 GMC Vandura, 1992 GMC Value Van, and 1992 GMC Suburban. However, it is still accessible from the selected car via links, so may be relevant.

The PCM/TCM monitors the difference in engine RPM and input shaft RPM. With transmission in Drive, scan tester reading should show engine speed closely matching input speed.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. Code 68 will set under the following conditions: engine speed is 200 RPM greater than input speed, 4th gear is indicated, TCC is enabled, or if all conditions are met for 2 seconds.
  2. This test monitors signal sent to the PCM/TCM from transmission.
  3. This test confirms engine RPM signal to PCM/TCM.
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