Chevrolet Equinox Service Manual: Electronic Ignition System Description Engine Control

The electronic ignition system produces and controls a high-energy secondary spark.This spark is used to ignite the compressed air/fuel mixture at precisely the correcttime. This provides optimal performance, fuel economy, and control of exhaust emissions.This ignition system uses an individual coil for each cylinder. The ignition coilsare mounted in the center of each camshaft cover with short integrated boots connectingthe coilsto the spark plugs. The driver modules within each ignition coil are commanded ON/OFFby the engine control module (ECM). The ECM primarily uses engine speed, the massair flow (MAF) sensor signal, and position information from the crankshaft positionand the camshaft position sensors. This controls the sequence, dwell, and timing ofthe spark. The electronic ignition system consists of the following components:

Crankshaft Position Sensor

The crankshaft position sensor works in conjunction with a reluctor wheel on the crankshaft(front mounted crankshaft position sensor) or a reluctor wheel that is part of theflywheel (rear mounted crankshaft position sensor). The engine control module (ECM)monitors the voltage frequency on the crankshaft position sensor signal circuit. Aseach reluctor wheel tooth rotates past the sensor, the sensor creates a digital ON/OFFpulse. Thisdigital signal is processed by the ECM. This creates a signature pattern that enablesthe ECM to determine the crankshaft position. The ECM uses the signal to determinewhich pair of cylinders is approaching top dead center based on the crankshaft positionsignal alone. The camshaft position sensor signals are used in order to determinewhich of these 2 cylinders is on a firing stroke, and which is on the exhaust stroke.The ECM uses this toproperly synchronize the ignition system, the fuel injectors, and the knock control.This sensor is also used in order to detect misfire.

The ECM also has a dedicated replicated crankshaft position sensor signal output circuitthat may be used as an input signal to other modules for monitoring engine RPM.

Camshaft Position Sensor

This engine uses a camshaft position sensor for each camshaft. The camshaft positionsensor signals are a digital ON/OFF pulse and output 4 times per revolution of thecamshaft. The camshaft position sensor does not directly affect the operation of theignition system. The camshaft position sensor information is used by the engine controlmodule (ECM) to determine the position of the camshaft relative to the crankshaftposition. By monitoringthe camshaft position and crankshaft position signals the ECM can accurately timethe operation of the fuel injectors. The ECM supplies the camshaft position sensorwith a 5-V reference circuit and a low reference circuit. The camshaft position sensorsignals are an input to the ECM. These signals are also used to detect camshaft alignmentwith the crankshaft.

The ECM also has a dedicated replicated camshaft position sensor signal output circuitthat may be used as an input signal to other modules for monitoring engine RPM.

Knock Sensor

The knock sensor system enables the control module to control the ignition timingfor the best possible performance while protecting the engine from potentially damaginglevels of detonation, also known as spark knock. The knock sensor system uses 1 or2 flat response 2-wire sensors. The sensor uses piezo-electric crystal technologythat produces an AC voltage signal of varying amplitude and frequency based on theengine vibration ornoise level. The amplitude and frequency depend upon the level of knock that the knocksensor detects. The control module receives the knock sensor signal through the signalcircuit. The knock sensor ground is supplied by the control module through the lowreference circuit.

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

If the control module has determined that knock is present, it will retard the ignitiontiming to attempt to eliminate the knock. The control module will always try to workback to a zero compensation level, or no spark retard. An abnormal knock sensor signalwill stay outside of the noise channel or will not be present. Knock sensor diagnosticsare calibrated to detect faults with the knock sensor circuitry inside the controlmodule,the knock sensor wiring, or the knock sensor voltage output. Some diagnostics arealso calibrated to detect constant noise from an outside influence such as a loose/damagedcomponent or excessive engine mechanical noise.

Ignition Coils

Each ignition coil contains a solid state driver module as its primary element. Theengine control module (ECM) signals the coil driver to initiate a firing event byapplying ignition control (IC) circuit voltage for the appropriate amount of timeotherwise known as dwell. When the voltage is removed the coil fires the spark plug.

Engine Control Module (ECM)

The engine control module (ECM) controls all ignition system functions and constantlycorrects the spark timing. The ECM monitors information from various sensor inputsthat may include the following components, if applicable:

Throttle position sensorEngine coolant temperature (ECT) sensorMass air flow (MAF) sensorIntake air temperature (IAT) sensorVehicle speed sensor (VSS)Transmission gear position or range information sensorsEngine knock sensorsAmbient pressure sensor (BARO)