Check engine light p0455 HELPP

Check the gas tank filler neck grommet. This grommet seals the filler neck. Fuel vapors are very hard on rubber parts. The rubber will get hard and brittle and then leak.

Look for rust through on the filler neck itself. Especially if there is a plastic rock guard. Water will get between the plastic and filler neck. Rust through is the result.

Another clue is fuel on the ground during re-fill.

Next check the vacuum lines from the throttle body to the right hand fender well. As said before, gas vapors are hard on rubber parts.

From here on, it gets messy as this can be a difficult problem to track.

Maybe. It won't pass smog testing unless all readiness tests are complete. To answer your question you will need to look to see if the readiness tests are complete. An ODB2 scanner is needed.

Most autoparts stores will do it for free.

My vote that the readiness tests will NOT be complete. The extended period of time is a give away.

The EVAP test is failing. However, because of other conditions, the PCM waits for the test to fail multiple times before the check engine light is "latched". When the tests are deferred, readiness tests are flagged "not complete".

No, No, No....

The "all readiness tests are complete" flag will be set when all of the tests are complete. If anything, the PCM say, WOW. 90 miles and there are still outstanding tests. Well that's a problem because they should have completed long before now. Set the check engine light.

If it was that easy to beat the system, everybody would reset the PCM and drive for 90 miles.

Regardless, your question can be answered by a 10 second scan. Stop guessing.

It's possible to get your own ODB2 reader for less than $20 bucks. Then you could drive around and scan it every 10 miles and find out one way or the other.

Pending codes are just as the name suggests. Some DTC's do not latch the check engine light the first time they occur. Hence the "pending" part. If the error does not re-occur, the pending DTC is removed.

If the pending DTC occurs again, it's latched. Latched DTC's light the check engine light (MIL).

To pass SMOG tests, the inspector normally looks for two conditions:

• MIL off
• all readiness tests complete.

Read the attached document on drive cycles. Careful reading of this document explains why it can take so long for and EVAP related problem to "latch" the MIL light. Note the parts about cold soak and how weather plays a part as well as how the car is driven.

Good luck gaming the system. If you find a trick that works, I'm sure there are others that would like to hear it.

IMO, the mental effort already wasted on trying to game the system could have been better spent on actually fixing your car.

I am having the same problem on my 97 Cobra. The vacuum line from the purge valve is not connected to the intake manifold causing the fuel vapor to release incorrectly and giving the same code. Also check the plug with three wires going into the purge valve that are located on the firewall.

dsmithwc04 said:

I am having the same problem on my 97 Cobra. The vacuum line from the purge valve is not connected to the intake manifold causing the fuel vapor to release incorrectly and giving the same code. Also check the plug with three wires going into the purge valve that are located on the firewall.

Click to expand...

FWIIW, the 96-98 has a very different EVAP system than the 99-04.

The 98 and older MY's have a purge flow sensor and purge solenoid mounted in the evap vapor lines near the firewall. The charcoal canister is located in the right hand fender well. On the 98 and older cars, the purge flow sensor fails a high percentage of the time.

The 99-04 MY Mustang has the VMV value in the right hand fender well. The charcoal canister and CV solenoid have been moved behind the rear left wheel near the gas tank.

The 99-04 system is able to detect a much smaller leak.

While the EVAP systems are very different in physical layout, the DTC code means the same. Namely, there is a leak somewhere in the system. The trick is to find out where.

I won't lie. It can sometimes be very difficult to find these. There isn't alot of pressure in the EVAP system. So if you are looking for something obvious, that's not always the case. Common sense says to start with the usual easy stuff and work up from there.

Regardless of the MY, check the gas cap. Next check the filler neck. These cars are getting old enough where rust through can be a problem. As stated before, gas vapors are very hard on rubber parts. If the seals are hard and brittle and leaves tons of black residue on your hands everytime they are handled, likely the lines are rotted from the inside.

Note, never use high pressure air in an attempt to locate an EVAP leak unless the air pressure is limited to 2 PSI. Yes that is (2) PSI! Anything over that is likely to blow out seals that were never designed for high pressure.