I own a 98 f-150 5.4 with 70,000 miles.

I get a check engine light (code p0455-large leak detected in evaporative emission control system).

replaced the gas cap with an after market 'stant' ( I believe was the manufacturer) brand. The check engine light went away for 4 days then came on again.

no obvious vacuum line leaks.

puzzled. any suggestions?

 

Gas cap if you're lucky. But from the Motocraft site:

(Phase 0 - initial vacuum pulldown):
First, the Canister Vent Solenoid is closed to seal the entire evap system, then the VMV or EVMV is opened to pull a 8" H2O vacuum. If the initial vacuum could not be achieved, a large system leak is indicated (P0455). This could be caused by a fuel cap that was not installed properly, a large hole, an overfilled fuel tank, disconnected/kinked vapor lines, a Canister Vent Solenoid that is stuck open, a VMV that is stuck closed, or a disconnected/blocked vapor line between the VMV and the FTPT If the initial vacuum could not be achieved after a refueling event, a gross leak, fuel cap off (P0457) is indicated and the recorded minimum fuel tank pressure during pulldown is stored in KAM. A “Check Fuel Cap” light may also be illuminated.

If the initial vacuum is excessive, a vacuum malfunction is indicated (P1450). This could be caused by kinked vapor lines or a stuck open VMV. If a P0455, P0457, or P1450 code is generated, the evap test does not continue with subsequent phases of the small leak check, phases 1-4. Note: Not all vehicles will have the P0457 test or the Check Fuel Cap light implemented. These vehicles will continue to generate only a P0455. After the customer properly secures the fuel cap, the P0457, Check Fuel Cap and/or MIL will be cleared as soon as normal purging vacuum exceeds the P0457 vacuum level stored in KAM.

And:

Note that a stuck closed VMV generates a P0455, a leaking or stuck open VMV generates a P1450.

And:

The Canister Vent Solenoid output circuit is checked for opens and shorts (P1451 or P0446), a stuck closed CVS generates a P1450, a leaking or stuck open CVS generates a P0455.

 

wow
thank you sir

 

You're welcome, I can cut and paste with the best of them.

 

Hi Mike and welcome to the forum

Quite often a P0455 is caused by a bad canister vent solenoid or broken wiring to it. If you look above the rear axle you'll see the canister vent solenoid. It is a cylinder shaped piece about umm 1.5" in diameter and 3" long or so. It has 1 electrical connector on it. Check the wiring to make sure it isn't broken or corroded at the connector.

 

Thanx again.
This site is great, very informative.

 

WHat's a VMV?
the purge valve under the hood?

 

I have a 2003 F150 5.4L 4x4. I'm throwing the same P0455/P0457 codes. Replaced the gas cap(OEM). cleared lights then they came on 4-6 days later. I have inspected all hoses visually.

Just wanted to bump this to see if anyone ever figured out what the cause of their problem was. This seems to be a popular issue with this make of 150's. On my canister above the spare tire i can see what i believe is a hose intake but no hoses in sight. Is this supposed to be wide open for the fresh air???

 

Have been working on 1999 ranger supercab for my son. This truck belongs to my son and had the PO455 code .After replacing fuel cap code came back. What I found out to be the problem was the fuel neck. The vent tube was half rusted off and at least 6 holes in the main tube. The problem was trying to find the right neck. My sons truck is equipped with a flareside or sterpside bed. All the necks I could find where for the regular or styleside bed. I found a neck on ebay with part # fn2 that said it was for styleside bed as well but was a little over 30.00. Not like all the other places that wanted at 100.00. For 30.00 I ordered it anyway figuring I would modify it to make it work. Received the neck it was a perfect fit, no mod needed.

 

Researching for a friend on her 2003 Ford F150 and wondering if the other canister purge valve not located above the rear axle can also pull those codes? When I bring up the part from autozone web site it shows the one above the axle as well as another that has two vacuum ports and a electrical port as well as two hole apparent screw down design. Any help would be well appreciated in fixing this issue with her truck.


Charles

 

The CANP valve is under the hood, usually on the firewall. It's the CANV valve that's mounted on the canister under the rear of the truck.

That fault can be caused by ANY leak in the system, whether from a faulty gas cap, a bad vent or purge solenoid, a rusted out filler or vent tube, a leaky gasket or hose coupling anywhere in the system.

Without a smoke test, it' really hard to find the leak.

 

same code I have read everything you all have posted and thanks so very much. can anyone tell me if I will be damaging the truck driving it with any of these issues that can be the cause of this leek (Code)? it just came on and I have to drive back and forth to Bmore
thanks
JM

 

The only thing it will affect is your ability to pass an emissions test, should you be required to take one.

Oh, and the tree-huggers will hate you for potentially polluting more.

 

I just bought the truck so I am thinking maybe they had cleared the code but we did get the test done after we bought it so would have thought it would not have passed so not sure, if it passed then I guess the leak just happened, just like the actuators that blew out on the ride home. but hey got them to pay for that. going to fix it as soon as the travel stops. thanks so much for the info

 

Could be as simple as needing a new gas cap (Motorcraft only is recommended). ... or not.