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Home >> GMC >> 1994 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - Electronic Transmission >> Trouble Code Charts >> Code 85, Undefined Gear Ratio >> Diagnostic Aids

Diagnostic Aids

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

GEAR RATIO SPECIFICATIONS

Gear Less Than More Than
1st 12.38 22.63
2nd 11.43 21.58
3rd 1.95 21.05
Reverse 11.97 22.17
Fig 1: Code 85 Schematic (4L80-E Diesel) Undefined Gear Ratio
G94G66064
Fig 2: Code 85 Schematic (4L80-E Gasoline) Undefined Gear Ratio
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Fig 3: Code 85 Flow Chart (4L80-E Gasoline) Undefined Gear Ratio
G94H66065
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