One problem that can vex even an experienced mechanic is the evaporative emission control systems on post 1996 cars and trucks. When we had our 1996 Ford Escort in for one of these issues, the dealer couldn't even differentiate between a "soft" and a "hard" code. It took me nearly three years to find out it was a $15 sensor for a purge sensor. All I needed for that fix was a hair dryer and ohmmeter to find that out, but I digress. Amateurs!
The specific problem is a code P0440 and/or a P0441. Both have to do with a evaporative emissions control flow fault. In plain English, this means the system isn't working to some degree. As anyone should know, gasoline is a highly volatile fuel, in that it vaporizes fairly easily. This stray vapor can leak out of the fuel system into air, causing smog and degrading air quality. At first it would seem sensible to just seal the fuel system and eliminate all the vents. The problem is (like those asinine child resistant gas cans with no vent that take a small eternity to pour. Note to self, keep the kids out of the gas), is that the gas tank would collapse and the engine would stall once half the fuel is used up. It would also burn up the fuel pump. The evaporative system allows air to rush in to equalize the pressure, but also keeps the fuel vapors where they belong, inside the system and the tank. This uses a charcoal canister, hoses, some kind of sensor and a valve to manage these and allow them to be burned when the engine is on.
The valve (or solenoid) in question on the Intrepid lives next to the brake master cylinder and has two hoses sticking out, along with an electrical connector. It also looks like a little black plastic trash can. Follow both hoses; one should go underneath the car to the charcoal canister, the other to the intake manifold on the engine. That that hose off, with the engine off, and try to blow through it. This should be impossible to do if the valve is closed, which it should be. Next, put the hose back on loosely and start the engine. Pull the hose and put your finger over the hole. Now blow into the hose; it should be very easy. If not, the solenoid is probably not working. Pull the wire connector, or back probe same and measure the voltage to the red wire. There should be 12 volts to one, If not, the computer or related wiring is messed up. Take to a service technician, or not.
If there is power, the valve is probably stuck and even if it does come on, the valve is sticking intermittently. You could replace the part for about $50, but I'm about saving money. You'll need two leads with alligator clips on both ends (preferably one with an inline fuse) a tube of die-electric tune up grease, and a screwdriver to pry the cover off the valve. Take out the valve and carefully pry the clips holding the cover to the valve. Then remove the spring and cups living inside and set them aside. DON'T LOSE THEM. Hook a wire to each terminal on the valve and ground one end. Tap the other end to the battery. The solenoid valve should pop up and promptly go down again while the power is cut off. More often than not, this valve will stick in the open position and this seems pretty likely if the engine has any blow by (what 2.7 liter doesn't, unless it's already trashed), not to mention the terrible heat this part is exposed to. As long as this works, even if it sticks, you can probably fix it. Take your grease and lubricate the solenoid shaft, pulling this in and out with your fingers (do not use pliers). Once you're satisfied this isn't going to stick, put the valve back together and hook it back up to the car. Use your code reader (you have a code reader, don't you?) to reset the code and turn off the "check engine" light. The results should be be nearly immediately realized if your code reader can tell you the evaporative emissions system is ready. If you don't you'll have to disconnect the battery and wait nearly a month for the light to come on, or not. If this checks out, your job is done. Maranatha!
Update, the light came on again. So back to square one.
Updated update, the canister purge soleniod is toast. I confirmed this by testing the voltage going to this part with the engine on. Then I blew through the hose that attaches to the soleniod from the engine. With the connector on and the engine on, I could not blow through it. Again, the solenoid is bad. I'm going to the boneyard in a few days and let you know how this shakes out in a future post.