GM Service Manual Online
For 1990-2009 cars only

Ignition System Overview

The ignition system consists of the following components or circuits:

    • The 8 ignition secondary wires
    • The 8 ignition coils
    • The 8 ignition control (IC) circuits
    • The camshaft position (CMP) sensor
    • The camshaft reluctor wheel
    • The crankshaft position (CKP) sensor
    • The crankshaft reluctor wheel
    • The related connecting wires
    • The powertrain control module (PCM)

Crankshaft Position Sensor and Reluctor Wheel


Object Number: 65872  Size: SH

The crankshaft position (CKP) sensor is a magneto resistive type sensor. The CKP sensor works in conjunction with a 24X reluctor wheel. The reluctor wheel is mounted on the rear of the crankshaft. The 24X reluctor wheel uses 2 different width notches that are 15 degrees apart. This pulse width encoded pattern allows cylinder position identification within 90 degrees of crankshaft rotation. In some cases this can be achieved within 45 degrees of crankshaft rotation. The reluctor wheel also has dual track notches that are 180 degrees out of phase, this design allows for quicker starts and accuracy. The CKP sensor also outputs a 4x signal for spark control, misfire diagnosis, tachometer output, and fuel control. All CKP signals are output as a digital square waveform.

Camshaft Position Sensor


Object Number: 690593  Size: SH

The camshaft position (CKP) sensor works in conjunction with 1x reluctor wheel mounted at the rear of the camshaft. The CMP is used to determine the top dead center position of cylinder #1, and will synchronize with the 24x CKP sensor signal for quicker starting. The PCM will detect an increase in the mass airflow (MAF) sensor signal when the engine starts. The CMP signals are output as a digital waveform.

Ignition Coils


Object Number: 703554  Size: SH

The ignition system on this vehicle features a multiple coil configuration and is known as coil near plug. There are two styles of ignition coil assemblies (1,2). The engine could have either style. The ignition coil mounting bracket is attached to the rocker cover (3).


Object Number: 260177  Size: SH

The 8 ignition coils are individually mounted above each cylinder on the rocker covers, the coils are fired sequentially. There is an ignition control (IC) circuit for each ignition coil . The 8 ignition control circuits are connected to the PCM, the PCM triggers each ignition coil individually and makes all timing decisions. The ignition coils are supplied with the following circuits:

    • The ignition 1 voltage circuit
    • The ignition control circuit
    • The ground circuit
    • The reference low circuit

The ignition 1 voltage circuits are fused separately for each bank of the engine. The 2 fuses also supply the power for the injectors for that bank of the engine. Each coil is serviced separately.

This system puts out very high ignition energy for plug firing. Less energy is lost to ignition wire resistance because the ignition wires are much shorter than in a conventional ignition system.

Circuits Affecting Ignition Control

To properly control ignition timing, the PCM relies on the following information:

    • The engine load, manifold pressure or vacuum
    • The atmospheric, barometric, pressure
    • The engine temperature
    • The intake air temperature
    • The crankshaft position
    • The engine speed (RPM)

The ignition control (IC) system consists of the following components:

    • The ignition coils
    • The 24X crankshaft position sensor
    • The powertrain control module (PCM)
    • All connecting wires

The ignition control utilizes the following to control spark timing functions:

    • The 24X signal--The 24X crankshaft position sensor sends a signal to the PCM. The PCM uses this signal to determine crankshaft position. The PCM also utilizes this signal to trigger the fuel injectors.
    • The ignition control (IC) circuits--The PCM uses these circuits to trigger the ignition coils.

Noteworthy Ignition Information

There are important considerations to point out when servicing the ignition system. The following noteworthy information will list some of these to help the technician in servicing the ignition system.

    • The ignition coils secondary voltage output capabilities are very high, more than 40,000 volts. Avoid body contact with ignition high voltage secondary components when the engine is running or personal injury may result.
    • The 24X crankshaft position (CKP) sensor is the most critical part of the ignition system. If the sensor is damaged so that pulses are not generated, the engine does not start.
    • The CKP sensor clearance is very important. If the interrupter ring is bent or damaged in any way, the CKP sensor may be destroyed. Extreme care must be exercised during removal and installation procedures.
    • The ignition timing is not adjustable. There are no timing marks on the crankshaft balancer or the timing chain cover.
    • Be careful not to damage the secondary ignition wires or boots when servicing the ignition system. Rotate each boot in order to dislodge the boot from the plug or coil tower before pulling the boot from the spark plug or the ignition coil.

Powertrain Control Module (PCM)

The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provide optimum driveability and emissions, the PCM monitors input signals from the additional following components in calculating ignition control (IC) spark timing:

    • The engine coolant temperature (ECT) sensor
    • The intake air temperature (IAT) sensor
    • The mass air flow (MAF) sensor
    • The trans range inputs from the transmission range switch (PRND)
    • The throttle position (TP) sensor
    • The vehicle speed sensor (VSS)