I keep getting an evap. system error code PO443. I have replaced purge valve and sensor and checked all the vacuum hoses. Is there a way to check if my gas cap is sealing properly? The cap and filler neck seal surfaces are smooth and clean, but I don't seem to hear any rush of air I think you should get when removing the cap after running the truck awhile, or does that depend on the type vehicle system? PO443 is a generic code. Thank's. Frank.

 

P0443 Evaporative Emission Control System Purge Control Valve Circuit

This is a "circuit" code so wiring or device issue

Full list of Ford OBD codes here: https://www.therangerstation.com/tec...II_codes.shtml

Computer has ALOT of codes to choose from so the codes it does NOT use mean as much as the code(s) it does use

For example if there was a leak it can use these
P0442 Evaporative Emission Control System Leak Detected (small leak)
P0455 Evaporative Emission Control System Leak Detected (gross leak)

But it didn't, thats not to say there is not a leak, there may be, but until Purge Valve is working it can't test for the leak

 

Thank you RonD for the reply. I'll check the system again. When I checked the purge valve originally, I wasn't hearing it open and close ( clicking sound) and the new one I tested did, so I was sure that was the problem. The next step, I replaced the purge valve sensor, which pretty much makes up the whole system, besides the vacuum hoses, which are fine. I haven't checked to see if the system is getting voltage from the computer yet, When I checked the valve for operation it was on the bench and not in the truck. Thank's again for the reply.

 

Most solenoids in a vehicle get 12volts with key on, and the computer uses the ground wire for control, it can use a Pulsed Ground(PWM) to fine tune how far a solenoid valve moves.

The "Circuit test" starts with, Does the computer "see" 12volts on that ground wire with key on, it should since a solenoid is just a coil of wire, so 12v in = 12v out
Then it will test if the solenoid is adjusting what it controls, in this case negative pressure in the gas tank, this takes awhile because it can only test while driving and then it has to run a few tests to confirm an issue

And it can also be a computer issue, so nothing you change on the outside can fix it, and there is no way to test for that, except what you are doing, check everything outside of the computer

Yes, you should hear a rush of air, into the tank, when removing gas cap to fill up after driving
If you haven't noticed that in awhile then it could be purge valve was not putting negative pressure in the tank while driving, or there is a leak in the system
First check that Purge valve HAS VACUUM available with engine running
Just pull the hose off with engine running to check
Solenoids can be tested with 9volt battery, they will "click" open and "click" closed, there is no Polarity, either terminal can be + or - , as long as it has both it will "open", then the spring inside will "click" it closed with no power

 

Thank's again RonD. Yes, I do have vacuum when I remove the line from my running engine. I remove the gas cap often when using truck, but still no rush of air. Perhaps I have a leak in the line going back to the tank, but as you mentioned, the computer would probably give me a different code. I have a makeshift smoke tester I made, that I used to find a small leak in my sons Kia mini van evap. system, but that was a small leak code. I haven't checked to see if I have voltage going to the purge valve with the key on yet, I would think that I should, as I mentioned earlier I was testing valve with it on the bench using a small 12 volt battery. I'll keep at it! Thank's for the help.

 

You can also use a hose and damp rag to check for air leak, and a second person
Take gas cap off
Put hose into filler and wrap damp rag around it, and hold it in place, to make a seal
Blow into the hose
Tank should hold pressure
Listen for escaping air if not

DO NOT use an air compressor for this, YOU WILL BLOW OFF EVAP FITTINGS, for sure
Lungs can generate about 2psi MAX., no air compressor can be turned down that low, lol

 

Thank' Ron, I would never think of that, I'll give it a try tomorrow.

 

I have a 96 also and got a similar code. P1443: Evaporative Emission System Control Valve (low/no flow). The possibilities were similar to what yours are. Gas cap didn’t change it. But I have since come up with an idea of what the issue is.

If I fill the tank beyond the first click-off of the gas pump I get gas dripping under the truck. It goes away quickly and if I stop when the pump clicks off – no leak. So I do have a small leak and my guess is a “return line”. Now I just have to find the time to drop the tank etc.

 

Thank you for the reply. I haven't had a chance to work on mine lately do to bad weather. I haven't seen any fuel leaking on mine as yet, I still have to check the vacuum line back to the tank, I may have damaged it working to replace the rusted brake line that runs between the fuel tank and frame rail, that is were the evap. line runs also. But I do know my tank is not holding any pressure. Thank's again.