Last Friday after fueling up I had a check engine light come on. Toggling the ignition revealed a P1693 code but there was no companion code displayed. After about 50-miles of driving and several engine starts, the check engine light went out and has stayed out. Now after 500-miles of driving (truck runs great), I can still retrieve a P1693 but no other codes. Does anyone have any idea what this might mean? I have always monitored the lift pump pressure and maintained safe levels. TIA