Principles Of Operation

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The ignition coils are supplied with electrical power from the battery via a 175 A megafuse in the BJB (battery junction box), the CJB (central junction box) and the ignition relay in the power distribution box. The control signal for the ignition relay is supplied by the CJB.

The ECM sends a separate signal to each ignition coil to trigger the power stage switching. The ECM calculates the dwell time from the battery voltage and engine speed, to ensure a constant energy level is produced in the secondary coil each time the power stage is switched. This ensures sufficient spark energy is available without excessive primary current flow, which avoids overheating and damage to the ignition coils.

The ECM calculates the ignition timing for individual cylinders from:

Engine speed
Camshaft position
Engine load
Engine temperature
The knock control function
The shift control function
The idle speed control function.