What does the code p0440 mean for 2003 PT Cruiser?

Answer 1

A P0440 code (GENERAL EVAP SYSTEM FAILURE) is typically one of two things... a huge evaporative system leak or a failed NVLD unit. The evaporative system is the vapor side of your fuel system. Vapors need to be contained, stored and burned just like liquid fuel does. An on-board leak detection system tests for overall performance of the evap system at practically any time in one manner or another. A leak could be as simple as a gas cap left loose. Actually, it takes a leak of almost this size to set a P0440. When fuel vapors can escape out the filler neck, they won't be stored in the vapor canister and a purge flow failure will result. This combines the two major components of the system (leak testing and purge flow) in failure mode, so the result is P0440. The natural vacuum leak detector (NVLD) is the device that senses whether the system is air-tight and confirms purge flow testing. It's nothing more than a device that can sense a weak vacuum/ low pressure condition in the evap system and then close an electrical switch to tell the PCM that all is well. If the NVLD has a failed switch, it doesn't matter that the system may be completely alright... it still has the appearance of failure. Start off looking for evaporative system leaks. The cap is the first stop. Check to see first if it was tightened properly. I like to lightly twist the cap counter-clockwise using just the spring built into the cap's top. If the cap is loose, it will come off using just this tiny bit of force. If it's been tightened, it won't. If it seems tight, remove it and check the rubber seal on the cap for cracking. Cracks are a sure sign that it's leaking, but probably not enough to cause a P0440. The vapor canister would be the next stop. It's under the truck, so inspect it for damage from road debris. A large (1/2" dia) hose connects the top of the canister to the NVLD unit. This hose typically cracks and falls off. A replacement hose runs less than $10. If no leaks are found at this point, I'd recommend replacing the NVLD. It's the odd black plastic unit with two 1/2" hose ports on it and a single 3-wire connector. The type of leak needed to set your code needs either a huge leak or a failed NVLD. With no leak, this is all that remains in the vast majority of cases. The exceptions? Very rarely, damage to the wiring harness can simulate a failed NVLD. Rodents can chew wiring practically anywhere and this little pigtail is no exception. The PCM (engine controller) has shown failure to sense the NVLD signal on rare occasions (I saw it one time).