Ignition System Check

Electrical:

CIRCUIT DESCRIPTION

The Catera 3.0L V6 is equipped with a Distributorless Ignition System (DIS). In this ignition system, both ends of each of the three ignition coils are connected to a spark plug. A pair of cylinders share one coil in the following arrangement: 1 and 4, 2 and 5, 3 and 6. Each coil is connected to spark plugs on companion cylinders, for example, on top center at the same time. One cylinder is on the compression stroke when the other one is on the exhaust stroke.

When the coil discharges, both of the plugs fire at the same time by using the engine block in order to complete the electrical circuit. The cylinder on the compression stroke is called the event cylinder and the cylinder on the exhaust stroke is called the waste cylinder. The two cylinders share the energy that is available from the ignition coil to tire both of the spark plugs. This method of ignition is called the waste spark ignition.

The Catera DIS system consists of the coil pack and the ECM. There is no separate ignition control module. The ECM performs all of the ignition control module functions. The Ignition Coil assembly is powered by an ignition feed circuit. The remaining three wires go to the ECM and are the Ignition Control (IC) circuits. The ECM causes a spark to occur by pulsing an IC circuit, which triggers an ignition coil and tires the appropriate pair of spark plugs. The ECM controls the sequencing and the timing.


DIAGNOSTIC AIDS

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

TEST DESCRIPTION

The number(s) below refer to the step numbers on the diagnostic table:

3. The scan tool output control commands the ECM in order to pulse the IC circuit to ground about 5 times per second. The Ignition control pulses have a very short pulse width (about 1 ms). The test light will blink with each pulse but will be dimly illuminated due to the very short on-time.

21. Recheck the system for multiple problems that may be related (for example, fouled spark plugs caused by the fuel system compensating for a misfiring cylinder).