What does it mean?
Here the second evaporative purge control valve is electrically sound but does not seal when it is commanded shut, so vapour keeps flowing into the engine at times the module never asked for. The evaporative system runs a pressure or vacuum test with the purge path closed; if the module cannot hold the expected pressure, or it sees a vacuum develop in the tank when purging should be off, it concludes the valve is leaking or stuck open.
Debris from a deteriorating charcoal canister is the classic reason, because carbon dust holds the sealing element off its seat. A valve that leaks continuously upsets the idle mixture, so fuel trims move and the engine may stumble on a hot restart. It also lets manifold vacuum reach the tank, which can cause unusual pressure readings and refuelling complaints.
Symptoms
- Rough or unstable idle, particularly after a hot restart or when the canister is loaded
- Stalling or a stumble as the engine returns to idle
- Long cranking after refuelling, sometimes with a burst of black smoke
- Fuel trim values swinging rich then correcting, visible in live data
- MIL (check engine lamp) on with evaporative leak or purge flow codes recorded alongside
- Hissing from the intake area at idle in quiet conditions
Likely causes
- Charcoal dust or debris from a broken down canister lodged on the valve seat
- Worn or hardened internal seal in the valve so it no longer closes tightly
- Solenoid plunger sticking in the open position due to varnish or contamination
- Weak internal return spring inside the valve
- Valve installed in the wrong flow direction or a hose routing error after service
- Cracked or split purge line allowing flow to continue past the valve
- Control circuit fault that keeps the valve energised, which must be excluded first
How to fix it
- Rule out an electrical fault first by checking that the valve is de energised at idle and that no purge command is present
- Watch tank pressure in live data with purge commanded off; a developing vacuum points directly at a leaking valve
- Remove the valve and test it with low pressure air in both directions, energised and de energised, to confirm it seals when closed
- Inspect the valve inlet for charcoal dust, which also means the canister itself must be examined for internal breakdown
- Check hose routing and the flow direction marking, since a reversed valve will not seal against manifold vacuum
- Replace the valve, and replace the canister as well if carbon migration is found, otherwise the new valve will fail the same way
- Clear the codes, allow fuel trims to relearn and run the evaporative monitor to confirm the system now holds