Beretta V6-3100 3.1L VIN M SFI (1995)
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3X reference low - CKT 453. This wire is grounded through the module and makes sure the ground circuit has no voltage drop between the
ignition module and the PCM, which if open, could affect performance.
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IC bypass-CKT424. During initial cranking, the PCM will look for synchronizing pulses from the camshaft and 3X crankshaft position
sensor indicating the position of #1 piston and intake valve. When 5 volts is applied to the bypass circuit the instant these signals are
received by the PCM. This generally occurs within 1 or 2 revolutions of the crankshaft. An open or grounded bypass circuit will set a
Diagnostic Trouble Code (DTC) 42 and the engine will run at base timing. A small amount of advance is built into the ICM to enhance
performance.
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IC - CKT 423. The PCM uses this circuit to trigger the electronic ignition control module. The PCM uses the crankshaft reference signal to
base its calculation of the amount of spark advance needed under present engine conditions.
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24X reference signal additional to the electronic ignition system is the 24X crankshaft position sensor. It's function is to increase idle
quality and provide good low speed driveability.
HOW DTC 42 IS DETERMINED
An open in the IC circuit while running will result in the engine continuing to run although in a base timing mode (module timing). The timing
values are stored in the ignition control module to allow for basic engine performance.
If the IC circuit is shorted to ground, the Malfunction Indicator Lamp (MIL) will be turned "ON," and a DTC 42 will be set and the engine will
operate in module timing. Either condition may cause poor performance and reduced fuel economy.
If the bypass line is open or grounded, the ignition control module will not switch to IC timing mode so the IC voltage will be low and DTC 42
will he set.
If the IC circuit is grounded, the ignition control module will switch to base timing and a DTC 42 will he set and MIL illuminated.
