Fault Line

Ignition System Circuit:

DESCRIPTION
The DIS fault line tells the PCM when the ignition module has detected a fault with the PCM inputs. In the normal logic state, the voltage in the fault line is "HIGH" (about 50% of battery voltage) with the ignition "ON". A change in the fault line to the "LOW" state (below 0.5 volts), indicates one of the following problems:

1. Faulty input to the DIS module from the PCM on the EST circuit.
2. Fault line circuit open between the DIS module and PCM (poor connection, broken wire)
3. Fault line circuit grounded between the DIS module and PCM.

The PCM can distinguish between condition 1 and conditions 2 and 3 by performing a "fault line check". When the fault logic goes "LOW" the PCM will pull the bypass circuit voltage "LOW". When this happens, the fault line voltage should return to its "HIGH" state. If it does not, a code 16 will be stored, indicating an open or grounded fault line circuit. The PCM will re-test the fault line a total of 10 times. If the fault line voltage does not return to the "HIGH" state, the PCM will store code 36 indicating an open or short in the EST line, or too many reference pulses have been detected.