GM Service Manual Online
For 1990-2009 cars only

Enhanced Ignition System Overview

The ignition system initiates combustion by providing a spark to ignite the compressed air and fuel mixture at the correct time. In order to provide an improved engine performance, fuel economy, and control of exhaust emissions, the control module controls the distributor spark advance, or timing, with the ignition control (IC) system.

The ignition system uses a primary and secondary sub system in order to accomplish the timed spark distribution. The primary system consists of a low voltage trigger device which determines the base timing. This signal is modified by the ignition control driver (ICD) module. The signal travels to either or both the engine and transmission processor (control module) for base timing reference. Another signal is sent back to the ignition control driver (ICD) module, which has been adjusted by the control module (advanced or retarded) in order to trigger the coil, according to the requirements of the engine.

The secondary system consists of the ignition coil which has primary, or low voltage, windings and secondary, or high voltage, windings. The secondary side of the ignition coil generates a high voltage which high tension spark plug wires deliver to the spark plugs.

The control module controller now controls the ignition control (IC) and bypass functions.

In order to properly control the ignition and combustion timing, the control module needs to know the following things:

    • The crankshaft position
    • The engine speed or RPM
    • The engine load -- manifold pressure or vacuum
    • The atmospheric or barometric pressure
    • The engine coolant temperature
    • The camshaft position sensor