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 MANUALSGMC1995SUBURBAN K2500, 7.4 NREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - 7.4LTROUBLE CODE CHARTSCODE 87, HIGH GEAR RATIO ERRORNOTES
1995 GMC Suburban K2500, 7.4 N
Code 87, High Gear Ratio Error: Notes
1995 GMC Suburban K2500, 7.4 NSECTION 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.
RENDER: 1.0x
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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.