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.
Code 42, Ic Circuit Open/Grounded: Notes
1994 Chevrolet Lumina BaseSECTION Notes
Code 42 indicates PCM has seen an open or short to ground in HEI EST or by-pass circuit.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
- This test checks for a normal IC ground path through ignition module. If EST circuit is shorted to ground, reading will be less than 500 ohms.
- As test light voltage touches by-pass circuit, module should switch. This will cause ohmmeter to switch from hundreds of ohms to thousands of ohms. This test assures module "switched".
- If module did not switch, this 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 PCM and not an intermittent problem in IC or 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.