P0440 EVAP fault code

Trey · Jul 27, 2009

I found this online and thought it would be good to post it here...

http://answers.yahoo.com/question/index?qid=20080424073326AAIfG2Q

First, and the most common problem with these are the gas caps being cracked or not sealed properly. This system has a pressure sensor in the tank for fuel vapor reasons. If you cap is loose or cracked the sensor will not read a buildup of pressure in the tank and then will register a code...P0440 Evap emissions fault. Second...don't take it to Amcco again...they are NOT specialists trained in inspecting and diagnosing this type of system. Try to find a dealership or a Subaru mechanic that knows these systems. This Evap system is VERY unique to Subura and the way the fault code is generated. You may have filled up two or three days ago and the code is now just appearing. It takes a few things for the test to be conducted by the ECM (engine control module)....the fuel tank has< about 9.5 gals fuel, vehicle speed over 28 mph, intake manifold vac must be equal to the vacuum one would get at cruising speed, fuel temp must be less than about 110-113 degrees and somewhere around 450-460 seconds has elapsed since engine was started. Now with all that done THEN the ECM runs a diagnostic over 2 trips and THEN trips the engine light. Pretty busy huh? Anyway the most common cause, per mechanics is the infamous gas cap...check it yourself to determine if the cap is cracked, the gasket that seats on the fuel intake is in good shape and the tether is not caught under the cap when tightened.

Beyond that you will need to have a tech do a tank pressure test (or sometimes a vacuum is pulled due to certain circumstances) on your fuel tank to see if there is a leak there. This will be followed by checking and inspection of the vacuum lines/hoses. On some subarus the charcoal evap canister is located in the back of car. The mechanic will then have to check the pressure control valve solenoid, the canister purge control valve solenoid and the canister vent valve for proper operation. The valve solenoids will "click" wen they are energized but make certain the mechanic physically pressurizes them to make certain that they open AND close completely! Sometimes they breeze through this and don't determine this.

What this system does is hold in the gasoline vapors that originate from the fuel injection system and gas tank...so they don't get out to the atmosphere. If any part of the system leaks or does not seal then an error code is given based on a 4 part test.
Step 1
You start and drive....Pressure solenoid comes on to determine if pressure is building in the fuel tank....as it should...which means the gas tank is properly sealed. Once the pressure changes then it goes to the next test. No pressure change then solenoid stays on looking for pressure in the tank to increase for the entire time you drive. It will not go on to the next testing protocol until if measures pressure change. So you see a loose gas cap will cause this to fail the test. Hence no pressure change and the computer will not go to diagnostic step 2.

Step 2
After 1 and after you are between about 45 and 75 or so cruising around AND your tank is less than 1/2 full!!!!!! The pressure control solenoid AND the Vent Solenoid come on at the identical time. If the PCS opens and reads pressure...if it gets a pressure differential reading then it passes. If not then.....you guessed it error to the ECM...if it does on to step 3
Step 3
Vent solenoid comes on which isolates the vent from the outside air and draws a vacuum across the entire evap system (pulls the gasoline vapors out so they can be burned). The pressure in the system and the tank should get down to around about -1.3 kPa (about 0.2 psi of vacuum)
If it does then the third part of the test is done
Step 4
The Vent solenoid will then close and pressure will again begin to increase in the fuel tank....just as you would expect as the fuel is heated and sloshes around...you get vapors produced and that produces pressure. Again the computer looks to see if there is pressure building in the tank.....None means....you guessed it fault code. If the pressure builds the compute senses it and then the last test has been passed and generates no fault code.

You can see that there are many places that this can go wrong and generate a fault code. Remember that this is just one code and there might be other problems also that weren't diagnosed because they weren't looking for them. The mechanics should be able to check this for you at the diagnostic rate but it will be most likely a $100 to $200 job. That said check your gas cap first, is the car tuned up with new plugs, timing set etc. They may want to check your fuel pressure and filter to make certain it is not a fuel related issue under all this also! I really hope this helps you! Any other questions just ask. Best
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lsnaple · Nov 4, 2009

I think I had this code before on my lgt, and just to let anyone know that if it isn't the gas cap check the hoses to the purge solenoid. Thought I needed a new one until I popped the hood and saw a hose had slipped of. Caused me a couple days of driving to ready the car for emissions.

Cool_____ · Nov 4, 2009

I've fixed about 4 of these codes on other peoples cars. Every one of them had the evap hose that runs into that tee under the intake manifold pulled off.

Trey · Nov 4, 2009

CoolRex said: ↑

I've fixed about 4 of these codes on other peoples cars. Every one of them had the evap hose that runs into that tee under the intake manifold pulled off.
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Pics? I get a code from time to time, no idea how to resolve it.

Cool_____ · Nov 5, 2009

No pics but it's all under the intake manifold behind the alternator. You will see several vac lines running under there and they go into a solenoid of sorts at a t.

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P0440 EVAP fault code

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