Powertrain Control Module (PCM)

The PCM maintains proper spark and fuel injection timing for all driving conditions. Ignition control (IC) spark timing is the method the PCM uses to control spark advance. To provide optimum driveability and emissions, the PCM uses the following circuits to calculate ignition spark timing:

• Low resolution engine speed signal
• Medium resolution engine speed signal
• Camshaft position
• Low reference
• IC timing signal
• IC timing control
• Knock Sensor (KS) signal

Low resolution engine speed signal is produced by the ICM. The PCM uses this signal to calculate engine RPM and crankshaft position above 1,200 RPM. The PCM also uses the pulses on this circuit to initiate fuel injector operation. The PCM compares the number of 3X pulses to the number of 18X and cam pulses. If the number of 3X pulses is incorrect while the engine is cranking or running, the PCM will set a DTC. Medium resolution engine speed signal is used to accurately control spark timing at low RPM and allow ignition control (IC) operation during cranking. The ICM calculates the 18X reference signal by filtering the 18X CKP sensor 1 pulses when the engine is running and the sync pulses from the 3X CKP Sensor 2 are being received. The PCM uses the Medium resolution engine speed signal for accurate ignition timing below 1,200 RPM. The PCM compares the number of 18X medium resolution engine speed signal pulses to the number of 3X low resolution engine speed signal pulses and 1X cam pulses. If the number of 18X pulses is incorrect while the engine is cranking or running, the PCM will set a DTC. The engine will continue to start and run normally using the 3X reference signal.

Camshaft position signal is used to determine the position of the cylinder #1 piston during the pistons power stroke. This signal is used by the PCM to calculate true sequential fuel injection (SFI) mode of operation. The PCM compares the number of 1X CMP Sensor signal pulses to the number of 18X medium resolution engine speed signal pulses and 3X low resolution engine speed signal pulses. If the number of medium resolution and low resolution engine speed signal pulses occurring between 1X CMP Sensor signal pulses is incorrect, or if no 1X CMP Sensor signal pulses are received while the engine is running, the PCM will set a DTC. If the 1X CMP sensor signal is lost while the engine is running the fuel injection system will shift to a calculated sequential fuel injection mode based on the last CMP sensor signal pulse, and the engine will continue to run. The engine can be re-started and will run in the calculated sequential mode as long as the condition is present with a 1 in 6 chance of being correct.

Low reference is used to provide a common reference between the ICM and the PCM. This is a low reference for the digital RPM counter inside the PCM; the wire is connected to engine ground only through the ICM. IC timing signal is used to control spark timing while the engine is cranking, this is called bypass mode. Once the PCM receives the 3X low resolution engine speed signal from the ICM, the PCM applies 5 volts to the IC timing signal circuit allowing the ICM to switch spark advance to PCM control.

IC timing control is used to control timing signals to the ICM on this circuit. When in the Bypass Mode, the ICM grounds these signals. When in the IC Mode, the PCM sends the signal to the ICM to control spark timing.

Knock Sensor signals is used to detect engine vibration or noise level.