For 1990-2009 cars

### 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

| OR

• | The engine is running.

### 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.