P0440 2000 Toyota Camry - why would Check Engine light go off by itself?

Question

Check engine light came on, vehicle taken to shop and diagnosed as PO440. Decided to wait until daughter drove car home to check it out for obvious before taking to shop for repair/reset. A few days later, the light went out by itself.

Answer 1

P0440 Evaporative emission control system malfunction

The purpose for the evaporative system is to trap raw fuel fumes into a charcoal canister and store to be consumed by the purge system of the evaporative system, When the CK ENG LT comes on the ECM detected a problem with the system, if the CK ENG LT went out ECM seen a correction.

 Most Evap codes are set due to failing to either properly secure the fuel cap or the fuel cap sealing is poor condition