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 MANUALSCHEVROLET1987HI-CUBE 6.2 J, 400/M40REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 16 (ENGINE CONTROLS - TESTS W/CODES - 5.0L)TROUBLE CODE CHARTSCODE 42 - IGNITION CONTROLNOTES
1987 Chevrolet Hi-Cube 6.2 J, 400/M40
Code 42 - Ignition Control: Notes
1987 Chevrolet Hi-Cube 6.2 J, 400/M40SECTION Notes
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Code 42 indicates ECM has seen an open or short to ground in the Ignition Control (IC) or by-pass circuits.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
- This tests for a normal IC ground path through ignition module. If circuit is shorted to ground, reading will be less than 500 ohms.
- As test light voltage touches by-pass circuit, module should switch. This causes ohmmeter to "over-range" with meter in 100-200 ohm range. A higher ohm range will indicate over 5000 ohms. This test assures module switched.
- If module did not switch, this step tests for a short in IC circuit, an open in by-pass circuit and a faulty ignition module connection or module.
- This step confirms Code 42 is a faulty ECM and not an intermittent problem in IC and by-pass circuits.
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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.