Powertrain, generic · Auxiliary emission controls
P04F0 EVAP System High Load Purge Line A Performance
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
Turbocharged engines also purge the charcoal canister under boost, through a high-load line to the compressor inlet via a venturi; check valves keep boost out of the EVAP system, and CARB requires this path to be monitored. P04F0 checks it: Ford (2020–23, replacing P144C) runs the test once per trip under boost with the vent closed and purge open, and sets the code if tank pressure rises faster than 0.5 or 1 inH2O/s or the vacuum rate is out of range, within 5–10 s. VW, Audi and Bentley monitor the line with their own pressure sensor.
Likely causes
Check valve in the purge line leaking, stuck open, fitted wrongly or missing
High-load purge line to the turbo or venturi off, cracked or blocked
Purge line pressure sensor wrongly connected or faulty (VW group)
Purge valve or venturi faulty
Symptoms
- Check engine light on
- Usually no change in driving
- Possibly fuel smell, EVAP readiness not set
Repair estimate
DifficultyMediumDIY possible
Parts and labour€30–300
Time0.5–2 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
high load purge linepurge check valvepurge venturifuel tank pressure sensor
Related codes
References: fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.