C 2500 Truck 2WD V6-262 4.3L VIN Z (1992)
Control Module: Description and Operation
Calculated Ratio
Undefined Ratio Circuit
Ratio is an input calculated by the PCM/TCM from the output and input speed sensor readings.
If the PCM/TCM calculates a ratio for gears 1st, 2nd and 3rd, that is inconsistent with the gear being commanded by the PCM/TCM, and the
condition lasts for over 2 seconds, Code 85 (undefined ratio) will set.
While code 85 is present, line pressure (force motor duty cycle) will be set to a default value. If the undefined ratio condition goes away, normal
transmission operation will resume after the next ignition cycle.
