Q: P1684

P1684 indicates that the engine control unit / powertrain control module memory was cleared at some point within the last 50 ignition cycles - start/drive/turn off. If the battery was replaced or disconnected, it can leave this fault code in the system. Also, if battery voltage dropped to a certain point either due to loose/dirty battery connections, the vehicle not being started for some time, or a battery replacement, this code may set and not indicate any real faults other than to indicate the ecm/pcm memory was cleared due to low voltage.The battery would not have had to be completely dead to set this fault, but simply dropped below a certain point. This code by itself will generally not set the check engine light on. If no other fault codes are present, check the battery voltage and connections. If the check engine light comes back on and sets any other fault codes besides the P1684, then have a certified technician follow the proper diagnostic path to determine the cause.