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: By-Pass Open Or Shorted: Notes
PCM has an internal feedback to monitor state of by-pass circuit. Code 42 will set if by-pass circuit is open, shorted to ground or shorted to voltage at time of engine start-up. If Code 41 is set with Code 42, use CODES 41 & 42 SIMULTANEOUS chart.
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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.