Snap-On scanner gives the FD code.
Codes P1684 and P0456 read over the odometer by cycling the key three times. P1684 simply means the memory has been cleared sometime in the last 50 ignition cycles. P0456 Evaporative System Small Leak Detected. Visually check the evaporative system for cracked or leaking hoses. Remove the vacuum hose from the top of the vent valve. Attach a hand vacuum pump to the vent valve and apply 20” Hg. vacuum. Observe the vacuum for 10 seconds. If the vacuum holds between 15.5” Hg. and 20” Hg., The valve is OK. If the vacuum drops below 15.5” Hg., replace the LDP Vent Valve.
See TSB # 25-001-02 Rev. A.