Ignition Coil: Operation
The Auto Shutdown (ASD) relay provides battery voltage to the ignition coil. The PCM provides a ground contact (circuit) for energizing the coil. When the PCM breaks the contact, the energy in the coil primary transfers to the secondary causing the spark. The PCM will de-energize the ASD relay if it does not receive the crankshaft position sensor and camshaft position sensor inputs. For limp home capability, the engine can run on crankshaft sensor or camshaft sensor. Refer to AUTO SHUT DOWN RELAY for relay operation.
The coil's low primary resistance (0.4 - 0.6 ohm) allows the PCM to fully charge the coil for each firing. There is a coil capacitor added to each bank of cylinders for the 2.7L and the left bank of the 3.5L for radio noise suppression (Fig 1 ).