P0440 - Evaporative Emission (EVAP) System
just popped up in my '02 STS tonight.
For past couple of days the DIC has been telling me "Check Gas Cap". I did, and tightened it again. TIGHT. So, any other possibilities?

 

after you tighten the gas cap clear the codes and see if it will come back. Other wise if the cap is tight the light will go off after awile.

 

yeah, believe me that's the first thing I did. popped back up. any fuel system leaks throw an EVAP code in the past? could it be something in exhaust, aka faulty O2 sensor? or is this contained to the fuel tank itself?

 

IIRC there is a sensor that senses pressure build up in the tank and when it gets to a certain point it releases some of the pressure by letting some of the fumes out into the engine. You dont have to worry about it causing the car to run differently but possibly see if the cap is cracked or sometimes if you dont push the cap down all the way and when you twist it will feel as if its on but not seal quite right. Im a lil stumped. since thats all ive had to ever do on my 2000 grand am, the cap on that is very hard to push down and i never quite get it tight all the time.

P0440 is a large leak in the EVAP system..alot of people call this the "gas cap code"
A O2 sensor will not fix the problem.
What has happend is the PCM (computer) has seen a leak in the EVAP sytem and has turned on the light.
Here is how the PCM runs the test
The evaporative emission (EVAP) system is checked by applying vacuum to the EVAP system and by monitoring for a vacuum decay. The Powertrain Control Module (PCM) monitors the vacuum level through the fuel tank pressure sensor signal. At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve will turn OFF, sealing the system. DTC P0440 will set because the PCM is not detecting the expected vacuum. This can be caused by the following components with the conditions listed below:

The fuel cap for the following conditions:
Missing
Malfunctioning
Incorrect
The fuel tank pressure sensor for the following conditions:
Disconnected
Malfunctioning
The EVAP purge line for the following conditions:
Disconnected
Damaged
Pinched
Blocked
The EVAP vent hose for the following conditions:
Disconnected
Damaged
The fuel tank vapor line for the following conditions:
Disconnected
Damaged
Pinched
Blocked
The EVAP canister purge solenoid valve for the following conditions:
Disconnected
Malfunctioning
The EVAP vent solenoid for the following conditions:
Disconnected
Malfunctioning
An open ignition feed circuit to the following components:
EVAP vent valve
Purge solenoid
A damaged EVAP canister
A leaking fuel sender assembly O-ring
A leak in the following items:
Fuel tank
Fuel filler neck


If you still are having problems i would recommend taking your car to a shop and have them diagnos the problem, the dealer has the tools necessary to diagnos the EVAP system properly and repair your problem.

 

I had the "Check Gas Cap" message on the DIC on my 01 STS.
So I checked It. It seemed to be ok but the message didnt go away. So on my way home I stopped at the dealer and purchased another one. Think it cost about 20 bucks. Havent had the message again in over a year.

Yes P0440 can refer to a few things. But if your getting the DIC message about the gas cap. Then I would start there.

 

Hi,

I was driving my car this morning, an 01' Deville and on my DIC it gave me the message "Check Gas Cap." But, the SES light did not pop on. So, the first thing I did is tighten the gas cap.

I normally get my gas in New Jersey as it's much cheaper than New York City. Jersey law prohibits to fill your own tank. So, it is always a gas jockey pumping the gas and putting your cap back on. I did notice that my cap did not seem to be flush.

So, I took it off and put it back in and made sure it clicked a few times. The SES light is not on and I get the message "Check Gas Cap" when I start my car. I used my OBD II scanner and I did have the P0440 code.

But, still no SES light, just the message "Check Gas Cap." This happened this morning. So, perhaps it will simply take time for the system to reset itself.

Does anyone have any thoughts on why there is no SES light, the DIC says Check Gas Cap?

Thanks for any help.