The electronic ignition (EI) module supplies a signal to the PCM whenever it determines that #4 cylinder fired on its compression stroke. Because of opposite coil tower polarity, the simultaneous fire of #1 and #4 cylinders are of opposite polarity as well. Under most conditions, except decel, the waste spark cylinder fires before the compression cylinder in sequence. The EI module can determine this polarity sequence and voltage amplitude by using capacitive pickup plates located under the 1/4 coil. If the module senses a positive to negative sequence and high negative spike when #4 is on TDC, it pulls the PCM cam signal to ground signaling that #4 has just fired on compression. This signal along with the double pulse received from the CKP sensor, synchronizes spark and fuel timing.

Important: The cam signal is continuously checked when the crankshaft sensor pulses are received by the PCM, except under deceleration.

Only one #4 signal should be received every 14 crank pulses. DTC P0341 will set if the cam signal received by the PCM is incorrect or has too many pulses per crankshaft revolution when:

Important: High resistance in the plug wire and connections, or plug will cause DTC P0341.

If an open circuit exists on the #4 cylinder, a DTC P0341 may set. This is due to the polarity and amplitude of the coil during every firing event looking as if the #4 cylinder is on compression. The PCM thinks the #4 cylinder is on compression every crankshaft revolution. Refer to misfire diagnostics if the engine has a misfire.