The distributor ignition system provides two timing inputs to the PCM, a high resolution signal (180 pulses per crankshaft revolution) and a low resolution signal (4 pulses per crankshaft revolution). One of the PCMs uses for these signals is to calculate spark timing. This timing signal is sent to the ignition coil module on the IC circuit. Each pulse on the IC circuit triggers the coil module to fire the ignition coil. The secondary ignition voltage then travels through the distributor to the spark plug. The IC signal voltage ranges from about 0.5 volt to 4.5 volts.

The PCM detects 84 crankshaft revolutions without any IC activity during cranking.

Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed. For intermittents, refer to Symptoms .

Number(s) below refer to step numbers on the diagnostic table.

3. The voltage fluctuates. This feature on the DVM will capture the minimum and maximum voltage of the signal.