The P1684 code simply means that the battery has been disconnected within the last 50 starts.
It would be very rare for a P1684 code to turn the light on.
From what I've found, the P1684 Code means that the ECU has lost voltage within the last 50 starts. This could be from disconnecting the battery, a loose or corroded connection, or even a weak battery from repeated or long cranking.
Trouble code P1684 means: The battery has been disconnected within the last 50 starts
What does code reading P1684 means for dodge neon car when you scan the engine
Trouble code P1684 means: The battery has been disconnected within the last 50 starts
P1684 - Transmission - Battery Power To Module Disconnected if battery was disconected for a while or battery replaced, it can cause to set this DTC
P0135-Right rear (or just) upstream O2 sensor heater failure P1684-The battery has been disconnected within the last 50 starts
Trouble code P1684 means: The battery has been disconnected within the last 50 starts P0601 is Internal Controller Failure- Common repair is Install new PCM and program it
Trouble code P1684 means: The battery has been disconnected within the last 50 starts
Trouble Code P1684 means:The battery has been disconnected within the last 50 starts
Trouble code P1684 means:The battery has been disconnected within the last 50 starts
Trouble code P1684 means: The battery has been disconnected within the last 50 starts