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Atypical P0455 Solution for 5.0

azstang

Member
Joined
January 4, 2005
Messages
33
Reaction score
4
City, State
Tucson, AZ
Year, Model & Trim Level
2000 XLT 5.0 AWD
Been troubleshooting DTC P0455 on my 2000 5.0 and finally found a non-typical failure that I wanted to share. Seems the most common cause for this code is a rusted out fuel filler neck causing a large leak in the EVAP system. Living in the desert southwest, the fuel filler neck on mine looks as good as it did the day Ford installed it 20 years ago so that wasn’t it. However, heat is an issue here and I eventually found the small rigid white plastic vacuum line that goes to the EVAP Purge Valve under the battery tray had disintegrated. This line is covered by split loom where it connects to the intake manifold so is hard to see the condition. I replaced the broken line with rubber vacuum hose and installed new split loom as shown below and that fixed it. Hopefully this will save someone a bunch of time!

Here’s a more detailed answer on why this fixed it if anyone is interested. The EVAP Purge Valve is normally closed and is commanded open by the PCM and manifold vacuum. The first self test the EVAP system performs when driving down the road is a pressure test (really a vacuum test). The PCM commands the normally open EVAP Vent Valve closed and opens the EVAP Purge Valve allowing manifold vacuum to lower the pressure in the EVAP system. The PCM then measures the pressure drop in the system using the Fuel Tank Pressure Sensor. Since the small vacuum line to the Purge Valve was broken, the Purge Valve never opened and the Fuel Tank Pressure Sensor never saw the reduction in pressure. This resulted in the PCM thinking there must be a large leak in the EVAP system and set code P0455. This one was very frustrating but very satisfying to finally solve!

EVAP 11.jpg


EVAP 12.jpg
 






Been troubleshooting DTC P0455 on my 2000 5.0 and finally found a non-typical failure that I wanted to share. Seems the most common cause for this code is a rusted out fuel filler neck causing a large leak in the EVAP system. Living in the desert southwest, the fuel filler neck on mine looks as good as it did the day Ford installed it 20 years ago so that wasn’t it. However, heat is an issue here and I eventually found the small rigid white plastic vacuum line that goes to the EVAP Purge Valve under the battery tray had disintegrated. This line is covered by split loom where it connects to the intake manifold so is hard to see the condition. I replaced the broken line with rubber vacuum hose and installed new split loom as shown below and that fixed it. Hopefully this will save someone a bunch of time!

Here’s a more detailed answer on why this fixed it if anyone is interested. The EVAP Purge Valve is normally closed and is commanded open by the PCM and manifold vacuum. The first self test the EVAP system performs when driving down the road is a pressure test (really a vacuum test). The PCM commands the normally open EVAP Vent Valve closed and opens the EVAP Purge Valve allowing manifold vacuum to lower the pressure in the EVAP system. The PCM then measures the pressure drop in the system using the Fuel Tank Pressure Sensor. Since the small vacuum line to the Purge Valve was broken, the Purge Valve never opened and the Fuel Tank Pressure Sensor never saw the reduction in pressure. This resulted in the PCM thinking there must be a large leak in the EVAP system and set code P0455. This one was very frustrating but very satisfying to finally solve!

View attachment 326213

View attachment 326214
Thank you for sharing man, i'm having the same error code and engine ligth went up yesterday about that aparently. I'll check it out!
 






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