P0455 1998 Ford F150 -computer won't command vent valve closed

Question

truck has po455 code, leak determined to be at canister vent valve, tried to command valve on with scan tool, still no valve actuation. Checked wiring to valve, has 12v at power wire, good continuity to computer for ground wire circuit. Tried alternate PCM, still no vent closing when commanded by scan tool. Vent valve has 58 ohms resistance.

Answer 1

There is a TSB for this situation 99-23-4 titled EVAP DTC P0442 / P0455. .What it has you to do is the EVAP running loss system monitor procedure  by monitor the FTP. If you bi directional the EVAP you read the FTP it should show a low to (-) number.This is a difficult code to troubleshoot the TSB sounds confusing but its on the right track.