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.
1995 GMC Forward Control 6.5 Y, AutomaticFACTORY OEM SERVICE PROCEDURE
Code 87, High Gear Ratio Error: Notes
Control module calculates ratio based on transmission input speed and output speed sensor readings. Control module compares known ratio to calculated ratio.
- An out-of-calibration transmission range pressure switch could falsely indicate actual transmission range.
- This test verifies proper ratio.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.