Wdt

= External watchdog, reset = Watchdog = WDT = interlock, this is a signal generated by the mcu that is observed by the 789101 supervisor IC. If the signal is absent/corrupt, the supervisor will reset the mcu. On one ECU (6Z68A), sabotaging the interlock signal while the ECU is running results in the nRST being pulled low a few times (apparently as attempts to restart the mcu), and then permanently pulled low after ~ 2 seconds. Restoring the interlock signal (with an external generator) is then ignored by the supervisor, only a hard (power-off) reboot will fix it.

The WDT signal is output from the PL5 pin of the mcu on many ECUs. It is typically accessible from testpoints on the PCB.

The signal itself is a 50% duty cycle pulse train @ 250Hz; this is 2ms high, 2ms low @ 5V TTL levels.

= WDT generator = Many simple circuits can generate an artificial pulse train, typically with a simple 555 circuit. [TODO - link/include PIC circuit