Bypass Signal

Ignition System Circuit:

DESCRIPTION
While the engine is being cranked (reference pulses being received and engine speed below 400 rpm) the PCM keeps the bypass circuit is in its low state and the ignition module controls spark timing. This is known as "bypass" or "module" mode because as long as there is no voltage signal in the bypass circuit, the ignition module ignores the EST signal from the PCM. In this mode, the ignition system operates independently of the PCM. Module mode spark advance is always at 6° BTDC plus a little preprogrammed advance based on engine speed. The PCM has no control of the ignition system when in this mode. If an PCM/EST fault is detected while the engine is running, the ignition system will switch to the module mode. The engine may quit running, but will restart and stay in the module mode with a noticeable driveability complaint.