Ignition Output Signal: Description and Operation

3X REFERENCE PCM INPUT (CKT 430)
From the ignition control module, the PCM uses this signal to calculate engine RPM and crankshaft position at engine speeds above 1200 RPM. The PCM also uses the pulses on this circuit to initiate injector pulses. If the PCM receives no pulses on this circuit, DTC P1374 will set and the PCM will use the 18X reference signal circuit for fuel and ignition control. The engine will continue to start and run using the 18X reference signal only.

18X REFERENCE PCM INPUT
From the ignition control module, the PCM uses this signal to calculate engine RPM and crankshaft position at engine speeds below 1200 RPM. The PCM also uses the pulses on this circuit to initiate injector pulses. If the PCM receives no pulses on this circuit, DTC P0336 will set and the PCM will use the 3X reference signal circuit at all times for fuel and ignition control. The engine will continue to start and run using the 3X reference signal only.

REFERENCE LOW
This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares voltage pulses on the 18X and 3X reference input circuits to any on this circuit, ignoring pulses that appear on both. If the circuit is open, or connected to ground at the PCM, it may cause poor engine performance and possibly a MIL with no DTC set. Refer to Ignition System for further information.

CAM Signal (CKT 630)
The PCM uses this signal to determine the position of the #1 piston during its power stroke, allowing the PCM to calculate true Sequential Multiport Fuel Injection (SFI). A loss of this signal will set a DTC P0341. If the CAM signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection based on the last fuel injection pulse and the engine will continue to run. The engine can be restarted and will run in the calculated sequential mode as long as the fault is present with a 1 in 6 chance of being correct. Refer to DTC PO341 CMP Sensor Circuit Performance. Testing and Inspection