Ignition Control (IC) System

Ignition System:

OPERATION
The distributor ignition system is a net build distributor (no timing adjustment) that provides angle based timing information to the Powertrain Control Module (PCM) for individual cylinder spark timing. The ignition module is capable of providing both 4X and 18OX timing pulses each crankshaft revolution. Using these timing pulses, the PCM processes ignition spark timing and sends an ignition control (IC) signal to the ignition coil module to activate the secondary ignition system.

The PCM provides power, ground, and two 5 volt reference voltages to the ignition control module. As the camshaft turns (during crank or run), a slotted two-track timing disk is rotated inside the ignition control module. Each time a slot in either track of the disk is properly aligned, the ignition control module will pulse one of the 5 volt reference voltages to ground.

A reference signal is generated each time the PCM detects that the reference voltages have been grounded by the ignition control module. When the PCM detects reference signals, ignition timing can be processed.

The PCM will also compare the 4X and the 180X signals to each other to determine the location of the number one cylinder and top dead center. In addition, if only one signal is being received by the PCM a Diagnostic Trouble Code (DTC) will be set. DTC 16 will be set if the 4X signal is missing and DTC 36 will be set if the 18OX signal is missing. The vehicle will not run if the 4X (REFERENCE) signal is not available at the PCM for processing.

IGNITION CONTROL (IC)
The Ignition Control (IC) system consists of the camshaft position sensor, ignition coil, ignition coil module, and PCM. The connector terminals are lettered as shown in CHART C-4.

These circuits perform the following functions:

Low resolution signal reference (CKT 453)
This provides the PCM with reference signals, firing order, and camshaft position information. If the low resolution signal circuit becomes open or grounded, the engine will not run because the PCM will not operate the ignition coil module, fuel pump, or the fuel injectors. A DTC 16 will set if the PCM receives high resolution signal references without the low resolution signals. If engine cranks but will not start refer to CHART A-3.

High resolution signal reference (CKT 430)
This provides the PCM with detailed reference signals and crankshaft position information. If this circuit becomes open or grounded a DTC 36 will set and the engine will still run, however, excessive crank times will be experienced.

Distributor reference low signal (CKT 632)
This circuit is grounded at the PCM and provides a redundant ground for the distributor.

Distributor ignition feed (CKT 631)
This circuit provides power to the distributor circuit. If this circuit becomes open, the engine will not run since there will be no reference information.

Ignition Control (IC) (CKT 423)
This circuit controls the ignition coil "ON" and "OFF" time. It signals the ignition coil module to begin primary coil dwell current when the IC is high. The ignition coil module shuts "OFF" ignition coil current when the signal goes low. If this circuit becomes open, shorted to voltage, or grounded, the engine will not start and a DTC 41 or 42 will set.

RESULTS OF INCORRECT OPERATION
An open IC circuit will set a DTC 41. A shorted or grounded IC circuit will set a DTC 42. An open or grounded IC circuit will result in a engine cranks but will not run.

An open or ground in the low resolution signal circuit will set a DTC 16 and the engine will not start. If the high resolution signal circuit becomes open or grounded a DTC 36 would set. This will cause reduced performance and poor fuel economy.

NOTICE: An inoperative distributor vent system may cause premature distributor failure, refer to CHART C-4C for distributor vent system diagnosis.