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 MANUALSCHEVROLET1987SUBURBAN R20, 7.4 N, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISCCC TBI TESTS W/CODESDIAGNOSTIC CHARTSMANUAL TRANSMISSION SHIFT LIGHT CHECKTEST DESCRIPTION
1987 Chevrolet Suburban R20, 7.4 N, 400/M40
Test Description
1987 Chevrolet Suburban R20, 7.4 N, 400/M40SECTION Test Description
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This should not turn the shift light on. If light is on, there is a short to ground in circuit No. 456 wiring, or a fault in the ECM.
- This should turn shift light on.
- This check for an open in the shift light circuit, or a faulty ECM.
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.