What does it mean?
The evaporative emission system carries fuel vapour from the tank through a line to the charcoal canister, where it is stored until the purge valve draws it into the engine. The module tests this path by commanding purge or by running the leak detection pump and watching how tank pressure responds. This code is stored when the tank vapour line does not allow pressure or vacuum to move as expected, meaning the line is kinked, crushed, iced or blocked by liquid fuel or debris. With the tank unable to breathe normally the system cannot complete its leak tests, and pressure builds inside the tank instead of being vented through the canister.
Symptoms
- MIL (check engine lamp) on with no obvious change in the way the vehicle drives
- A hiss or rush of pressure when the fuel filler cap is opened
- Difficulty refuelling, with the pump nozzle shutting off repeatedly
- Fuel smell around the rear of the vehicle
- A brief stall or stumble immediately after refuelling
- The evaporative readiness monitor never completing, which blocks an emissions inspection
Likely causes
- Vapour line kinked, crushed or pinched, often after underbody work or impact damage
- Liquid fuel trapped in the line, typically caused by repeated overfilling of the tank
- Rollover or vent valve at the tank blocked or stuck closed
- Charcoal canister saturated, or its inlet plugged with carbon dust
- Ice or water inside the line in cold climates
- Mud, debris or insect nests obstructing the vapour path
- Line damaged or wrongly routed after fuel pump or tank service
How to fix it
- Check the freeze frame for fuel level and temperature, since this test only runs under specific conditions
- Read tank pressure live and watch whether it responds when the purge valve is commanded open
- Inspect the vapour line along its entire length for kinks, crush damage, melted sections and incorrect routing
- Disconnect the line at both ends and verify it flows freely with low pressure air, watching for liquid fuel draining out
- Test the rollover and vent valves at the tank and check the canister inlet for restriction
- Replace or reroute the damaged line, clear any trapped liquid, and advise the driver not to overfill the tank
- Repeat the system test with a scan tool and confirm the tank now responds normally to purge