Q: was getting PO440 CODE.

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getting po440 code on 2001 s10 4cyl.changed vacum lines ,took off and checked vent and purge valves ,they operated as they should off vehicle ,but when put back on would not work. Had 11 volts at plug in to valves. What could be cause of valves not functioning.

My car has 99000 miles.
My car has a manual transmission.

These valves are controlled by the PCM so the circuit will not be closed until commanded by the PCM and that closure can be through the ground side. If the circuit is competed through the ground side, you will always be able to detect battery voltage if you measure the solenoid plug hot side to body ground, but if you check continuity on the plug side ground to vehicle ground you will find the circuit open simply because the solenoid is not supposed to be commanded on at the time you are checking for operation. The bottom line is if the solenoids test OK off the vehicle, re-install them and look elsewhere for the problem. You might want to check the wiring though because 11 volts is a little low, unless the battery is also low. You should see close to battery voltage at the solenoids. If not, there is too much resistance in the circuit.

Often code P0440 will set because the gas cap is not sealed or working properly, the purge solenoid has failed or the canister is faulty (plugged, etc.). Check the cap (ideally use a new OEM cap, not aftermarket) and erase the code and see what happens. If the code comes back, you may have to use a smoke machine to check for EVAP system leaks. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an EVAP system/canister diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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