Riviera V6-3.8L VIN K (1996)
3X REFERENCE PCM INPUT
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.
CAMSHAFT POSITION PCM INPUT
The PCM uses this signal to determine the position of the cylinder #1 piston during its 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 CAM pulses to the number of 18X and 3X reference pulses. If
the number of 18X and 3X reference pulses occurring between CAM pulses is incorrect, or if no CAM pulses are received while the engine is running,
the PCM will set 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 mode based on the last cam 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.
BYPASS SIGNAL PCM OUTPUT
The PCM either allows the ignition control module to keep the spark advance at Bypass Mode 10 degrees BTDC, or the PCM commands the ignition
module to allow the PCM to control the spark advance (IC Mode). The ignition control module determines correct operating mode based on the
voltage level that the PCM sends to the ignition control module on the bypass circuit. The PCM provides 5 volts on the bypass circuit if the PCM is
going to control spark timing (IC Mode). If the PCM does not apply 5 volts to the bypass circuit, or if the ignition control module does not sense the 5
volts, the ignition control module will control spark timing (Bypass Mode).
IGNITION CONTROL (IC) PCM OUTPUT
The IC output circuitry of the PCM sends out timing pulses to the ignition control module on this circuit. When in the Bypass Mode, the ignition
control module grounds these pulses. When in the IC Mode, these pulses are the ignition timing pulses used by the ignition control module to energize
one of the ignition coils. Proper sequencing of the 3 ignition coils, i.e.; which coil to fire, is always the job of the ignition control module.
