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 MANUALSCHEVROLET1997FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)TRANSMISSIONAUTOMATIC TRANSAUTOMATIC TRANSMISSION DIAGNOSIS - 4L80-E (2-DIGIT CODES)DIAGNOSTIC TESTSDTC 87: HIGH RATIO ERRORDIAGNOSTIC PROCEDURES
1997 Chevrolet Forward Control 5.7 R, Automatic
Diagnostic Procedures
1997 Chevrolet Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
- Connect scan tool to DLC. Turn ignition switch to ON position. DO NOT start engine. Using scan tool, record freeze frame and failure records for reference. Data will be lost when DTCs are cleared later in this test.
- Start and run engine until at normal operating temperature. Idle engine and apply parking brake. Select each gear position and observe scan tool. If each gear position matches scan tool TFP position switch A/B/C display, go to next step. See TFP RANGE SIGNAL TABLE . If each gear position does not match scan tool TFP position switch A/B/C display, go to DTC 28.
- Raise and support vehicle. Start engine and shift transmission into "D4". Using scan tool, command 1st, 2nd, 3rd and 4th gear while accelerating vehicle. If 1st gear was commanded but not achieved, or 4th gear was commanded and another gear occurred, go to next step. If all gears were commanded and achieved, see DIAGNOSTIC AIDS.
- Check shift solenoid hydraulics for internal malfunction at one or both solenoids. Check for damaged seals. Repair as necessary, then go to next step.
- After repair is complete, select DTC on scan tool. Select "Clear Info" function. Select "Specific DTC" and enter DTC 87. Operate vehicle under the following conditions: PCM/TCM must detect correct gear ratio for each gear for more than one second in "D1", "D2", "D3" and "D4". Hold throttle angle at more than 12 percent and accelerate to 55 MPH. If DTC 87 is not present, repair is complete. If DTC 87 is still present, repeat test.
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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.