Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1992SUBURBAN 3/4 TON 2WD V8-454 7.4LREPAIR AND DIAGNOSISTRANSMISSION AND DRIVETRAINAUTOMATIC TRANSMISSION/TRANSAXLECONTROL MODULEDESCRIPTION AND OPERATIONCALCULATED RATIO
1992 Chevrolet Suburban 3/4 Ton 2WD V8-454 7.4L
Calculated Ratio
1992 Chevrolet Suburban 3/4 Ton 2WD V8-454 7.4LSECTION 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.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.