Code 85, Undefined Gear Ratio: Notes

WARNING: This page does not describe the selected car, but rather 18 other vehicles, including the 1995 GMC Vandura Special, 1995 GMC Vandura, 1995 GMC Suburban, 1995 GMC Rally Camper Special, and 1995 GMC Rally. However, it is still accessible from the selected car via links, so may be relevant.

While in each gear, control module calculates actual gear ratio from input and output speed readings, also referred to as vehicle speed, then compares these to what gear ratio should be, taking into consideration selected gear range. This monitor includes reverse gear, but does not include overdrive gear.

NOTE: Test numbers refer to numbers on diagnostic chart.

An out-of-calibration transmission range pressure switch could falsely set Code 85.
This test verifies proper ratio.