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.
Diagnostic Aids
When attempting to diagnose an intermittent problem, use scan tester to review supplemental diagnostic information. Supplemental data (scan tester MALF HISTORY) can be used to help duplicate an intermittent problem. Using Diagnostic Service Probe (12092782) allows voltage to be read on wires without disconnecting connectors.
PCM will hold IC low if RPM reference is not received from ignition module. PCM resistance with no IC output is about 14,000,000 ohms. If using scan tester, 41A or 41B will display at end of general information table. A 41A indicates IC circuit is open, 41B indicates IC circuit is shorted to ground or voltage. If Code 41 is set with Code 42, use CODES 41 & 42 SIMULTANEOUS chart.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.