P0496 Evaporative Emission (evap) System Flow During Non Purge

Code: P0496
Applies To: Most makes, generic code
Loose Cap Can Set It: Not named in our sources
Typical Fix: $210 to $251 at RepairPal

Fuel vapor is flowing into the engine when the purge valve should be shut. This usually points to a purge valve that is stuck open.
A shop confirms it with the carmaker's EVAP test and a smoke machine before replacing parts.
Usually yes for now, but get it fixed soon and check for open recalls.

What The Carmakers Call It

Evaporative Emission (EVAP) System Flow During Non Purge, as printed by General Motors
EVAP System High Purge Flow, stuck open, as printed by Maserati S.p.A.

Where sources differ. GM calls it flow during non purge. Maserati calls it high purge flow, stuck open.

Causes Named In Carmaker Bulletins

A purge valve stuck by oil or contamination from the cam cover gasket (2014 to 2018 Impala 3.6L) (source)
Check the purge valve connector and wiring for oxidation and loose pins (Maserati) (source)

No source ranks these by how often they happen, so they are listed as the bulletins give them.

No source ties P0496 to the gas cap.

What The Fix Costs

The usual part for this code is the purge valve. Published estimates put it at $210 to $251 at RepairPal. The full table with every source and date is on the cost page. A diagnosis first keeps you from paying for a part you did not need, which is why we price what to do after a failed smog check before the fix.

Getting The Light To Go Off

After the repair the light goes off once the EVAP test runs and passes on three drive cycles in a row, and the code is erased after 40 warm up cycles, per CARB. The test only runs under set conditions such as a fuel level between about 15 and 85 percent, so it can take days.