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.
Modes Of Operation
Anytime the PCM does not apply 5 volts to the IC timing signal circuit, the Ignition Control Module (ICM) controls ignition by triggering each coil in the proper sequence at a pre-calibrated timing advance. This is called Bypass Mode ignition used during cranking or running below a certain RPM, or during a default mode due to a system failure. When the PCM begins receiving 24X reference and 3X reference pulses, the PCM applies 5 volts to the IC timing signal circuit. This signals the ICM to allow the PCM to control the spark timing. This is IC Mode ignition. During IC Mode, the PCM compensates for all driving conditions. If the IC mode changes due to a system fault, the system will stay in default until the ignition is cycled OFF/ON, or the fault is no longer present. DTCs are available to accurately diagnose the ignition system with a scan tool.
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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.