DTC P0340: Cam Sensor Circuit: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2001 Saturn SW2, 2001 Saturn SL2, 2001 Saturn SL1, 2001 Saturn SL, and 2001 Saturn SC2. However, it is still accessible from the selected car via links, so may be relevant.
The Electronic Ignition (EI) module supplies a ground to the cylinder No. 4 wire whenever it determines cylinder No. 4 has just fired on its compression stroke. EI module uses capacitive pick-up plates located under 1/4 coil pack to determine polarity sequence and voltage amplitude of cylinders No. 1 and 4 secondary ignition. PCM supplies 5 volts on signal line and expects to see cylinder No. 4 signal wire go low after every 14 crankshaft pulses (2 revolutions). This is used to determine position of camshaft, except under decel. PCM only uses transition from 5 to zero volts as a valid TDC compression cylinder No. 4 signal. DTC sets when PCM detects missing cam pulses (not seeing one cam pulse every 2 crankshaft revolutions).