Circuit Description
The electronic ignition (EI) module supplies a signal to the PCM whenever it
determines that the #4 cylinder fired on its compression stroke. Because of
opposite coil tower polarity, the simultaneous fir 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.
Conditions for Setting the DTC
Important: The cam signal is continuously checked when
crankshaft sensor pulses are received by the PCM, except under deceleration.
DTC P0340 will set if the PCM voltage on cylinder #4 signal wire is not
pulled to ground (cam signal pulse) when:
| • | The engine has been cranking for 5-10 seconds |
Diagnostic Aids
Important: A cam pulse missing may not affect engine
operation.
| • | An open or high resistance on the #1 plug wire or plug will result in
DTC P0340 setting. |
| • | Inspect the EIS towers and plug the wire connections for corrosion or
other signs of poor retention at connections. |
