Check Engine Light

I am having a Check Engine Light problem lately...It came on two times now at the exact same point of coming home from work 4 days apart...I took it in and it came up code 440 a fuel evaporative problem...I have always been filling my car while it was running and it just now started to come on...When I took it in they turned off the light and said my computer may have ran a test at the same time I was filling it...So he turned the light off but 4 days later the light came back on again...I replaced the cap just in case and he turned off the light again...Now will the light keep coming on until it runs through a certain amount of cycles?...I mean the car runs absolutly great even with the light on...I filled the car once with the engine off after the first time the light was turned off but it came back on...Thats why I am curious if it has to run through a certain cycle...That way if it comes back on I will just wait for it to go back off...Last thing is,Will filling it with the car running actually read a leak if it runs a test while filling it and if so I must have been lucky for 3 years that it didnt happen until now...Please let me know if anyone has any answers...Thanks alot...

Hey Twstr988....

My friend had a 1991 chevy lumina and the check engine light came on at the same time every time she drove it...her's was every second day after about 10 minutes of driving it. She took it to four mechanics and even her husband looked it over. It turned out it was just a sensor or something that went weird and there was nothing wrong with the car she had about 4 error codes all for fuel but nothing was wrong..she even spend a lot of money to replace parts. she was superstitious and didn't want to disconnect the sensor because she thought that would be when there was a problem with the engine...so maybe don't worry. if nothing wrong with u'r car and the mechanics don't seem to worried maybe you have a crazy sensor too.. hopefully that little story will help.

toxic_3186 (bc,canada)

I appreciate the feedback...Thats kinda what I thought might be the problem...It hasnt come back on yet in a couple days but if it does i will give it a little time to see if it clears itself and will check into relays and sensors if need be...thanks alot for the reply...

I am having a Check Engine Light problem lately...It came on two times now at the exact same point of coming home from work 4 days apart...I took it in and it came up code 440 a fuel evaporative problem...I have always been filling my car while it was running and it just now started to come on...When I took it in they turned off the light and said my computer may have ran a test at the same time I was filling it...So he turned the light off but 4 days later the light came back on again...I replaced the cap just in case and he turned off the light again...Now will the light keep coming on until it runs through a certain amount of cycles?...I mean the car runs absolutly great even with the light on...I filled the car once with the engine off after the first time the light was turned off but it came back on...Thats why I am curious if it has to run through a certain cycle...That way if it comes back on I will just wait for it to go back off...Last thing is,Will filling it with the car running actually read a leak if it runs a test while filling it and if so I must have been lucky for 3 years that it didnt happen until now...Please let me know if anyone has any answers...Thanks alot...

P0440 DTC is for a large leak detected in the EVAP system.
You need to have the EVAP system tested and the source of the leak found and repaired.
Turning the light off does not fix the problem

Um....taking the gas cap off while it's running IS a large EVAP leak....It'll set a code.

Um....taking the gas cap off while it's running IS a large EVAP leak....It'll set a code.

Correct, but doing some diagnostics to determine if the EVAP system is intact and there is not another underlying problem makes good sense.


P0440 description and operation
The EVAP large leak test applies vacuum to the evaporative emission (EVAP) system and monitors vacuum decay. The powertrain control module (PCM) monitors the fuel tank pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP vent valve ON (closed). This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, DTC P0440 will set.

Conditions for Running the DTC
DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0452, or P0453 are not set.
The ignition voltage is between 10-18 volts.
The barometric pressure (BARO) is more than 75 kPa.
The fuel level is between 15-85 percent.
The engine coolant temperature (ECT) is between 4-30°C (39-86°F).
The intake air temperature (IAT) is between 4-30°C (39-86°F).
The start up ECT and IAT are within 9°C (16°F) of each other.
The vehicle speed sensor (VSS) is less than 121 km/h (75 mph).

I just took my car in today go the exact same reason. My check engine light came on, but ran it's normal..horrible way. They said the same thing. Hope it is fixed. Good luck.

Actually I think it is Amoco gas when they came out with their new summer fuels...Because my brother in law has a Chevy and the day he put it in his light came on as well with the same code as mine did...I am going to look a little more into it and if there is a problem there may be a class action lawsuit against Amoco coming...Please post to this message if anyone else would maybe like to help me look into this as well as maybe trying to put this into motion if it is Amoco gas messing up our emissions components...I thought it might have been the gas but didnt think it was possible until I heard about my brother in laws car...Let me know if anyone has had the same problem after putting in Amoco gas... My car is running only on Shell now but the light still comes on so who knows if it might be to late and it has already messed up something in my car...Just let me know though...Thanks everyone...

more then likely just a bad gas cap :naughty:

Already replaced the gas cap...Nothing changed...