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.
Circuit Description
Each ignition coil supplies secondary voltage to a pair of spark plugs. This is called a waste spark ignition system. The Powertrain Control Module (PCM) supplies a signal on each of the Ignition Control (IC) timing control circuits to the Ignition Control Module (ICM). The ICM fires the correct ignition coil at the correct time based on the signals. The ICM detects if cylinder No. 1 or 3 is on the compression stroke by sensing the secondary voltage and polarity of each side of the ignition coil. The ICM detects this voltage with sensing circuitry integrated into each ignition coil. The higher voltage is on the compressing cylinder. This is called compression sense ignition. The ICM provides a synthesized cam signal to the PCM based on these inputs. The PCM uses the cam signals to synchronize fuel injection.
This system consists of the following circuits:
- Ignition voltage.
- Ground circuit.
- Camshaft Position (CMP) sensor signal.
- IC timing control for cylinders No. 1 and 4.
- IC timing control "B" for cylinders No. 2 and 3.
- Low reference circuit.
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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.
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