Home ReviewsRefund
Home/Chevrolet/C3500 HD/Chevrolet C3500 HD (1991-2000)/Repair manual/Engine Controls - Tests W/codes - 7.4l/CODE 85, UNDEFINED GEAR RATIO
Contents Section: Engine Controls - Tests W/codes - 7.4l All sections

CODE 85, UNDEFINED GEAR RATIO Chevrolet C3500 HD

Engine Controls - Tests W/codes - 7.4l 2 illustrations ~155 words

CODE 85, UNDEFINED GEAR RATIO

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.

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

Code will set when an unknown gear ratio is detected for any gear but 4th. Check all connections, especially those at transmission pass-thru connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES - GASOLINE article. Compare scan tester gear ratio reading to specifications in GEAR RATIO table.

GearLess ThanMore Than
1st12.3822.63
2nd11.4321.58
3rd1.9521.05
Reverse11.9722.17

GEAR RATIO

Code 85 Schematic (All Models) Undefined Gear Ratio. Scheme 264

Scheme 264: Code 85 Schematic (All Models) Undefined Gear Ratio
Scheme 264: Code 85 Schematic (All Models) Undefined Gear Ratio

Code 85 Flow Chart (All Models) Undefined Gear Ratio. Scheme 265

Scheme 265: Code 85 Flow Chart (All Models) Undefined Gear Ratio
Scheme 265: Code 85 Flow Chart (All Models) Undefined Gear Ratio