Emission controls · Powertrain · generic (SAE-defined)
P0496: Evaporative Emission System High Purge Flow
P0496 means the engine computer detected fuel vapor purge flow from the evaporative emission (EVAP) system when it was not commanded, usually from a purge valve stuck open.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0496 sets
With the purge valve commanded closed, the powertrain control module (PCM) watches the fuel tank pressure sensor. If the tank is pulled into vacuum, indicating engine vacuum is reaching the tank through the purge path, the PCM concludes purge flow is excessive and sets P0496. Test conditions are manufacturer-specific.
Common causes of P0496
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Purge valve or solenoid stuck open
- Purge valve leaking internally
- Wiring short keeping the purge valve energized
- Faulty fuel tank pressure sensor giving false vacuum readings
- Charcoal debris lodged in the purge valve
P0496 symptoms
- Check engine light on
- Hard starting, especially right after refueling
- Rough idle or stalling
- Possible lean or rich fuel trim codes
How P0496 is diagnosed
- Check for other EVAP, fuel trim, or tank pressure sensor codes
- With the engine idling and the purge valve not commanded, check for vacuum at the canister side of the purge hose
- Remove the purge valve and check whether it holds vacuum when de-energized
- Command the purge valve with a scan tool and confirm it opens and closes
- Check the control circuit for a short to ground
- Inspect for charcoal debris, which suggests a damaged canister
Typical fixes for P0496
- Replace the purge valve
- Replace the charcoal canister if it is breaking down and shedding debris
- Repair a shorted control circuit
- Replace a faulty fuel tank pressure sensor
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Commonly reported on GM and Chevrolet vehicles, including some small cars and trucks, where purge valves stick open. Definitions can vary by manufacturer; check factory service information.
Related codes & warning lights
P0496 FAQ
What does code P0496 mean?
P0496 means the engine computer detected fuel vapor purge flow from the evaporative emission (EVAP) system when it was not commanded, usually from a purge valve stuck open. The standard definition is "Evaporative Emission System High Purge Flow."
Can I drive with a P0496 code?
Usually yes, but a stuck-open purge valve can cause rough idle, hard starting after refueling, and occasional stalling. Have it repaired soon, as raw fuel vapor can also overload the charcoal canister.
Why is my car hard to start after filling up with gas?
A purge valve stuck open lets heavy fuel vapor from the canister flow into the intake during starting, flooding the engine with an overly rich mixture.
Should I replace the canister along with the purge valve?
Only if there is evidence of damage, such as charcoal granules in the purge lines. Otherwise, the valve alone is often enough.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.