[OsirisGuy]

Going to class this morning and they came on. I know I've gotten the P0456 code twice before this at random times and usually after I washed the car or did something, cleared them and they didn't come back. First time the CEL has come on when driving.

So the codes are:
P0442 EVAP Emission controle system leak (small)
P0456PD EVAP Emission control system leak very small.

I'd look them up and get a better idea then ask everyone here but I have lecture in 20 mins. I never really understood the xxxxxPD codes and just took them as codes that have recently been triggered or that have not gone through the whole system testing each time, i.e. the problem was registered right away with the computer.

I'll have a break soon enough and do a Google search on it, but has anyone ever seen these before? Is the diagnostic lengthy or can it be attributed to just something silly. I'm thinking it is a loose vacuum line or something.

 

[SaleenFiend]

Try your gas cap. Have you filled up with gas recently?

 

[OsirisGuy]

I always make sure my cap is tight, as for filling up I actually haven't even driven the car in 2 weeks or so. I'm at about 1/4 tank now. Maybe I'll pull the whole cap off and give it a good clean. I'd like to eventually get a locking cap too.

 

[SaleenFiend]

Well since your pretty certain on your gas cap. You could start by checking all the Evap Hoses and lines coming off of the gas tank and trace them for any damage or disconnection along them. You will probably need to get the car to someone who can do a leak detection test and maybe even a smoke test for the evap leak. I hate small leaks as they can sometimes take hours to find. It's also possible that a soleniod or valve failed on the evap system.

 

[OsirisGuy]

Gathered some more information:

P0442:
This indicates a fuel vapor leak in the EVAP control system. It means a very small leak has been detected. In fact, the leak can be from a hole as small as 0.04" in diameter. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.

Causes: A code P0442 most likely means one or more of the following has happened:
•A loose or improperly affixed gas cap
•A non-conforming gas cap (i.e. not factory/original brand)
•A small leak/hole in a fuel vapor hose/tube
•Other small leak in EVAP system
•Faulty vent o-ring seal

Possible Solutions: With a P0442, the most common repair is to:
•Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
•Otherwise, replace the gas cap, or
•Inspect the EVAP system for cuts/holes in tubes/hoses

P0456:
The Powertrain Control Module (PCM) at different times performs various tests on the EVAP system. OBD II Enhanced EVAP systems are in place to keep fuel tank vapors from venting into the atmosphere, and instead purges them into the engine to be burned. Regular pressure tests are conducted by the PCM to monitor the sealed system for leaks. The PCM monitors the EVAP system pressure by watching the Fuel tank pressure sensor (FTP). When the sensor indicates a small leak in the EVAP system, this code is set.

Potential Symptoms: There will likely be no noticeable symptoms other than the Malfunction Indicator Lamp (MIL). This is because the EVAP system is a closed system and only controls fuel tank vapors, not engine management.

Causes: Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivable cause this code as well or if the cap wasn't properly tightened. Any of the following could also be the cause:
*A small leak in any of the EVAP hoses or fuel tank hoses
*A small leak in the purge valve or vent valve
*The EVAP Canister may be leaking

Possible Solutions: First, using a scan tool activate the vent solenoid, sealing the system. Then monitor the fuel tank pressure (FTP) sensor. If the system is sealing properly, the number will stay consistent. If is isn't, the pressure sensor will show that as well. If the system slowly leaks, use a smoke machine and watch for smoke exiting the system at any EVAP component. Any where there is smoke exiting the system, that is the faulty component. Do not pressurize the EVAP system with air.

The "PD" is a 'Pending Code' or 'continous monitor' and 'maturing' codes.
Pending Codes: These codes are also referred as “continuous monitor” and “maturing codes”. An intermittent fault will cause the computer to store a code in memory. If the fault does not occur within 40 warm-up cycles, the code will be cleared from memory. If the fault occurs a specific number of times, the code will mature into a DTC and the MIL will turn on.

 

[FritzTheDev]

Necro'ing this thread in case future searchers find it helpful. This article goes over some common causes & fixes for P0456 on the mustang. (I ran into the very similar P0455 on my '06 V6 convertible). It's basically always an issue with the gas cap but if you're sure that's not it, the EVAP hoses are another possible culprit. They can crack as they get old.