Chevrolet Cobalt Service & Repair Manual: Description

Chevrolet Cobalt Service & Repair Manual / Engine Management / Ignition Systems / Description

This ignition system uses one coil for each pair of cylinders. Each pair of cylinders that are at Top Dead Center (TDC) at the same time are known as companion cylinders. The cylinder that is at TDC of its compression stroke is called the event cylinder. The cylinder that is at TDC of its exhaust stroke is called the waste cylinder. When the ignition coil is triggered, both companion cylinder spark plugs fire at the same time, completing a series circuit. Because the lower pressure inside the waste cylinder offers very little resistance, the event cylinder uses most of the available voltage to produce a very high energy spark. This is known as waste spark ignition. The ignition coils and ignition control module (ICM) are contained within one assembly. The ignition coil/ICM assembly is mounted in the center of the engine camshaft cover, with short boots connecting the ignition coils to the spark plugs. The ignition coil driver modules within the ICM are commanded ON/OFF by the Powertrain Control Module (PCM).

The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel has seven machined notches, six of which are equally spaced 60 degrees apart. The seventh notch is spaced 10 degrees after one of the 60-degree notches. The 10-degree notch (sync pulse) is used to synchronize the engine position, while the other notches are used to provide cylinder location during a revolution. The Crankshaft Position (CKP) sensor is a permanent magnet generator, known as a variable reluctance sensor. The CKP sensor produces an AC voltage of different amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC voltage output depends on the crankshaft position and the battery voltage. The CKP sensor works in conjunction with the reluctor wheel. The CKP sensor produces 7 pulses for each revolution of the crankshaft. The sync pulse is used to synchronize the coil firing sequence with the crankshaft position. The Powertrain Control Module (PCM) uses the CKP sensor signal for ignition timing, fuel injector timing, misfire diagnostics and tachometer display. The CKP sensor is connected to the ECM by a signal circuit and a low reference circuit.

The PCM supplies a signal on each of the ignition control timing control circuits to the ignition control module. The ignition control module fires the correct ignition coil at the correct time based on the signals. The control module detects if cylinder No. 1 or cylinder No. 3 is on the compression stroke by sensing the secondary voltage and polarity of each side of the ignition coil. The control module detects this voltage with sensing circuitry integrated into each ignition coil. The higher voltage is on the compressing cylinder. This is called compression sense ignition. The control module provides a synthesized cam signal to the PCM based on these inputs. The PCM uses the cam signal to synchronize fuel injection.

The knock sensor (KS) system enables the PCM 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 (spark knock).

Ignition Systems

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System Service

Component Replacement Ignition Control Module (ICM) 1. Remove accelerator cable from bracket. 2. Remove accelerator cable bracket bolt ...

Chevrolet Cobalt Service & Repair Manual: Description

Ignition Systems

System Service

See also:

Chevrolet Cobalt Owners Manual

Chevrolet Cobalt Service Manual