The ignition coil is used to provide the high voltage necessary to generate a spark across the spark plugs. It is basically a large transformer or "Tesla coil". By charging up the primary winding with 12V and then suddenly dropping it to zero, a large voltage is generated on the secondary winding. The high voltage on the secondary is directed to the correct spark plug wire through the rotor in the distributer cap.
The primary winding is supplied with 12V through the ASD relay circuit and is grounded through the power module. The logic module turns on the driver inside the power module, which supplies the coil with ground. When the appropriate spark timing is reached for this cylinder, the logic module shuts off the driver, which removes the ground and the secondary coil generates the high voltage for the spark.
When the logic module is turning on or off the coil driver, it momentarily checks the output of the output transistor to see if it is responding the way it should. If it does not see about 0V when on (open circuit) or 12V when off (short circuit), a fault code 43 is stored and the engine will stall.
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Copyright © 1996-2003 Russ W. Knize.