P0496: Evaporative Emission System High Purge Flow
The EVAP system is pulling fuel vapor into the engine when it should not be, usually because the purge valve is stuck open.
What P0496 means
The purge valve should only open when the engine is warm and running under the right conditions. RepairPal explains that when the computer detects the EVAP system purging when it should not, it sets P0496, and lists purge solenoid failure, wiring issues and a computer fault as causes. Tank pressure sensor replacement is also a common repair. The usual story is a purge valve stuck partly open from debris or carbon from the canister. With the valve open, engine vacuum pulls on the tank all the time, which the pressure sensor sees as unexpected vacuum. After a fill up, the canister is loaded with vapor, so a stuck open valve dumps that vapor into the intake at start up, causing long cranking, rough idle or stalling. A rich fuel trim code may show up too. Shops command the purge valve closed and watch tank pressure, and test the valve with a hand vacuum pump. Replacing the valve is usually a quick job.
Common symptoms
- Check engine light on
- Hard starting, especially right after refueling
- Rough idle or stalling
- Reduced engine performance
- Fuel smell
Most common causes
- EVAP purge valve stuck open
- Purge valve wiring shorted so it stays on
- Faulty fuel tank pressure sensor
- Damaged charcoal canister passing liquid fuel
- Engine computer fault (rare)
What to check yourself first
If the car is hard to start right after filling up, mention that to the shop, since it is a classic sign of a stuck open purge valve. With the engine off, try blowing through the purge valve; if air passes when it is unpowered, it is likely stuck open.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace EVAP purge valve | $210-$251 | RepairPal lists purge solenoid failure as the top cause. |
| Replace fuel tank pressure sensor | $356-$457 | RepairPal lists fuel tank pressure sensor replacement as a common repair. |
| Replace EVAP canister (includes vent valve on many cars) | $558-$643 | If charcoal or liquid fuel has damaged the canister. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | For a shorted purge valve circuit. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
Related repair guides
- Tundra in Limp Mode With Code P2440 or P2442? The Air Injection Pump Problem Explained
- Ram 1500 Ticking on Cold Start? Broken Exhaust Manifold Bolts, Repair Cost and What to Ask
Related codes
- P0441 Evaporative Emission System Incorrect Purge Flow
- P0443 Evaporative Emission System Purge Control Valve Circuit
- P0172 System Too Rich (Bank 1)
- P0451 Evaporative Emission System Pressure Sensor/Switch Range/Performance
- P0455 Evaporative Emission System Leak Detected (large leak)