Evaporative-emissions system
Evaporative-emissions system: The EVAP system stores fuel vapor in a canister; the ECU meters vapor to the intake through the purge valve and manages atmospheric connection through the vent valve. The page also includes a worked example and measurement sequence.
Technical frame
Evaporative-emissions system: The EVAP system stores fuel vapor in a canister; the ECU meters vapor to the intake through the purge valve and manages atmospheric connection through the vent valve. The page also includes a worked example and measurement sequence.
The technical values here expose the standard, protocol or physical relationship directly; model-specific service values are linked through the matching model/variant dossier.
The goal is not only to define the term but to let the reader calculate and interpret what the data means in a scan, scope or physical test.
Concrete technical facts
- The EVAP system stores fuel vapor in a canister; the ECU meters vapor to the intake through the purge valve and manages atmospheric connection through the vent valve.
- The purge valve can be PWM-controlled, and command changes can influence tank pressure and short-term fuel trim.
- Leak monitoring uses low differential pressure/vacuum; excessive external test pressure can damage tanks or valves.
- The tank-pressure sensor should start plausibly at KOEO/ambient conditions and respond smoothly to purge/vent commands.
- An electrical click from the purge valve does not prove flow or sealing; closed leakage and open flow need separate checks.
- Cap/filler neck, hoses, canister, purge and vent leaks can lead to similar monitor results.
Worked example
- Example: if purge command rises from 0% to 40%, tank pressure changes and STFT briefly moves negative, two independent signals support actual purge flow.
Measurement and verification sequence
- Log tank pressure, purge command, vent command and fuel trim together.
- Verify purge-valve closed sealing and open flow separately.
- Use a low-pressure smoke test to locate the physical leak path.
- Measure valve supply/driver current under command.
Fault-separation logic
- Is a valid command present and are power/ground/network healthy?
- Does feedback follow the command?
- Does an independent physical measurement confirm the output?
- Is the fault limited to a specific temperature/load/speed condition?
- Does the result remain stable when the original condition is repeated after repair?
Technical sources
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