P0496
EVAP System High Purge Flow.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 4
- AreaAuxiliary emission controls
- 96
- FaultThe specific fault in that area
What it means
P0496 means the evaporative emission (EVAP) system has detected purge flow when none should be happening, or more flow than the control unit commanded. The control unit usually sees this during a monitor test with the purge valve closed, when the fuel tank pressure or vacuum reading rises where it should stay steady or when the fuel trims shift unexpectedly. The most common cause is a purge valve that is stuck open or leaking.
Symptoms
- Engine warning light on
- Long crank or hard starting after refuelling
- Rough or unstable idle, especially just after starting
- Occasional stalling at idle
- Fuel smell around the car or engine bay
- Failed emissions test
Possible causes
- Purge control valve stuck open or leaking internallylikely
- Purge valve wiring fault, such as a short to power, or a connector problem causing the valve to stay openpossible
- Faulty fuel tank pressure sensor giving a false readingpossible
- Cracked, split or incorrectly routed EVAP hoses or pipes affecting the purge flow pathpossible
- Charcoal canister damaged or saturated with fuel, or a blocked or faulty vent valve causing abnormal pressure or vacuumpossible
- Control unit fault driving the purge valve incorrectlyrare
How to diagnose
- Read the stored and pending codes and the freeze frame data, noting engine temperature, load and fuel trim values when the fault set.
- Check for other EVAP, fuel trim or fuel tank pressure codes, as these help separate a valve fault from a sensor or leak problem.
- Visually inspect the purge valve, its connector and wiring, plus the EVAP hoses between the engine, the valve and the canister, looking for damage, chafing or loose fittings.
- With the engine off, check whether the purge valve is stuck open by testing for airflow through it with no power applied. It should be closed. The exact test varies by model.
- Use a scan tool to command the purge valve on and off and listen for it clicking. Watch for changes in idle, fuel trims and tank pressure.
- Measure the purge valve's supply, control signal and coil resistance against the manufacturer's specification for that engine.
- Check the fuel tank pressure sensor readings against the expected values with the system sealed and then vented, following the model-specific procedure.
- Inspect the canister and vent valve for liquid fuel, blockage or damage, and carry out a smoke test if a leak or restriction is suspected.
How to fix
- Replace the purge control valve if it is stuck open or leaking.
- Repair or replace damaged wiring or connectors in the purge valve circuit.
- Replace the fuel tank pressure sensor if it gives readings that are not plausible.
- Replace cracked, split or disconnected EVAP hoses and pipes, and make sure they are routed correctly.
- Replace the charcoal canister or vent valve if it is damaged, blocked or contaminated with fuel.
- Once the cause is fixed, clear the code and run a drive cycle to confirm the EVAP monitor passes.
Can I keep driving?
Low severity
The car can normally be driven while you arrange a repair. However, a purge valve stuck open can cause a rough idle, stalling or hard starting, so get it checked soon if those symptoms get worse.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.