The electronic ignition (EI) system produces and controls the high energy secondary spark. This spark ignites the compressed air/fuel mixture at precisely the correct time, providing optimal performance, fuel economy, and control of exhaust emissions. The powertrain control module (PCM) primarily collects information from the crankshaft position (CKP) and camshaft position (CMP) sensors to control the sequence, dwell, and timing of the spark.

The crankshaft reluctor wheel is mounted in the middle of the crankshaft. The wheel is comprised of three 120 degree segments. Each segment represents a pair of cylinders at top dead center (TDC), and is further divided into six 20-degree segments. Within each 20-degree segment is a notch of 2 different sizes. Each 120 degree segment has a unique pattern of notches. This is known as pulse width encoding. This pulse width encoding pattern allows the powertrain control module (PCM) to quickly recognize which pair of cylinders are at TDC. The reluctor wheel is also a dual track, or mirror image, design. This means there is an additional wheel pressed against the first wheel with a gap of equal size to each notch of the mating wheel. When one sensing element of the crankshaft position (CKP) sensor is reading a notch, the other is reading a set of teeth. The resulting signals are then converted into a digital square wave output by the circuitry within the CKP sensor.

The crankshaft position (CKP) sensor is a 3-wire sensor based on the magneto resistive principle. A magneto resistive sensor uses 2 magnetic pickups between a permanent magnet. As an element such as a reluctor wheel passes the magnets, the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The CKP sensor returns a digital ON/OFF pulse 24 times per crankshaft revolution. The pulse width encoding pattern is used to synchronize the coil firing sequence with the crankshaft position. The CKP sensor is used for ignition timing, fuel injector timing, misfire diagnostics, and tachometer display. The powertrain control module (PCM) supplies a 12-volt reference, a low reference, and a medium resolution engine speed signal circuit to the CKP sensor.

The camshaft position (CMP) sensor signal is a digital ON/OFF pulse output once per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor information is used by the powertrain control module (PCM) to determine the position of the valve train relative to the crankshaft position. By monitoring the CMP and crankshaft position (CKP) signals, the PCM can accurately time the operation of the fuel injectors. The PCM supplies the sensor with a 12-volt reference circuit, a low reference circuit, and a signal circuit.

The knock sensor (KS) system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The control module uses the KS system to test for abnormal engine noise that may indicate detonation, also known as spark knock.

The KS system uses one or 2 flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the KS detects. The control module receives the KS signal through the signal circuit.

The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal KS signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal KS signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near top dead center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel.

If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal KS signal will stay outside of the noise channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the control module, the KS wiring, or the KS voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise.

There are 3 dual-tower ignition coils that are part of the ignition control module (ICM). The ICM contains coil driver circuits that command the coils to operate. The ICM has the following circuits:

The powertrain control module (PCM) controls each dual-tower ignition coil by transmitting timing pulses on the ignition control (IC) circuit to the ICM for the proper coil to enable a spark event.

The spark plugs are connected to each coil tower by spark plug wires. The spark plug wires conduct the spark energy from the coil to the spark plug. The spark plug electrode is tipped with platinum for long wear and higher efficiency.

The powertrain control module (PCM) controls all ignition system functions, and constantly corrects the basic spark timing. The PCM monitors information from various sensor inputs that include the following:

There is one normal mode of operation with the spark under powertrain control module (PCM) control. If the crankshaft position (CKP) pulses are lost, the engine will not run. The loss of a camshaft position (CMP) signal may result in a longer crank time since the PCM cannot determine which stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.