Evap code 0440

Shortly after replacing the gas tank, sending unit, and fuel pump on my 1997 Lesabre, I started getting a "bumping" sound from the tank expanding. Lots of pressure escaping when refilling. I replaced the gas cap as that is the most common reason. But it still throws the code. I have checked that it is sucking form the switch over the valve cover and have tried to seal off any vacuum leaks. Any suggestions for a cure? Thanks, Ron

Welcome to AF.

DTC P0440 is a large or gross leak in the evaporative emissions system. Normally associated with a bad gas cap seal but I guess not in your case. When the fuel pump was replaced how was the pump to gas tank seal? Another possibility is a loose or damaged evap line that feeds into the top of the fuel pump assembly or back to the cannister.

Brand new seal! How is all the pressure building up if there is a gross LEAK? Maybe a blocked line? The cannister is clear, checked it out last night. But I've read about the vent solonoid at the cannister; will try to replace it. Also, there is a sensor(?) on top of the tank near the sending unit tha I transferred when I changed the tank. It has a elec. connector from the harness feeding the send. unit. Could that be faulty? Thanks, anything else you can think of?

Could be a blocked or disconnected line or the system not venting or purging properly. The malfunction criteria for DTC P0440 setting is tank vacuum <7.9" of H20. I think the sensor you are referring to is the tank pressure sensor which must function properly for the test to come out good. The one at the engine is the purge solenoid/valve.

Here's some info on odb-ii DTC error code P0440, EVAP Emission Control System Malfunction which may be helpful to you:

The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay. The PCM monitors vacuum level via the Fuel Tank Pressure sensor input. At an appropriate time, the EVAP purge valve and the EVAP canister vent valve are turned ON, allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. If a sufficient vacuum level cannot be achieved, a large leak or a malfunctioning EVAP purge valve is indicated. This can be caused by the following conditions:

Disconnected or malfunctioning fuel tank pressure sensor.
Missing or malfunctioning fuel cap.
Disconnected, damaged, pinched, or blocked EVAP purge line.
Disconnected or damaged EVAP canister vent hose.
Disconnected, damaged, pinched, or blocked fuel tank vapor line.
Disconnected or malfunctioning EVAP purge valve.
Disconnected or malfunctioning EVAP canister vent valve.
Open ignition feed circuit to the EVAP canister vent or purge valve.
Damaged evaporative emissions canister.
Leaking fuel sender assembly O-ring.
Leaking fuel tank or fuel tiller neck Any of the above conditions can set DTC P0440.

CONDITIONS FOR RUNNING THE DTC

No VSS, TP sensor, HO2S, Misfire, IAT sensor, MAP sensor, Fuel Trim, Fuel Injector(s), EGR Pintle Position, ECT, or MAF sensor DTC(s) set.
Start up engine coolant temperature is between 4°C and 30°C (40°F and 86°F).
Start up intake air temperature is between 4°C and 30°C (40°F and 86°F).
Fuel tank fuel level is between 15% and 85%.
BARO is greater than 75 kPa.
System voltage is between 8 and 16 volts.

Car runs excellent!!

Where pressure be coming from? I wonder if maybe a fuel injector can leak and a cylinder compression backflow into the tank?

The pressure comes from engine manifold vacuum which is used to test the evaporative emissions system. I seriously doubt it is a fuel injector leak or engine compression backflow to the tank which is one of the most ridiculous replies I have heard this year. :rolleyes:.......:shakehead

Thanks BNaylor, I don't want to bash anyone trying to help me out, but although my electronics knowledge is weak, I know just about everything else about a car. Am going to cheak out a few things you referred to this weekend, Thanks again.

I thought my reply at post #4 was self explanatory. Unless anyone can come up with any better suggestions that is the best I can do to help. :dunno: Good luck and let us know how it turns out.

BTW - To clarify:


Vacuum is negative, and pressure is positive. Pressure does not come from vacuum. If what you are saying is true you may have a positive pressure on the tank and it is not venting into the evaporative “vacuum” purge system. When fuel expands, it creates a positive pressure and in turn, the purge system pulls a vacuum to stabilize that pressure. Ideal conditions, would be negative, or a slight vacuum on the fuel tank.