: Question on a code....

05-07-07, 01:21 PM
Okay I went and got gas today and left the car running...not a norm but okay no big deal. Then when I opened the cap you heard the gases leaving like usual when running a tank too low. Then when I got back in the car reset the trip got service Engine Light.
pulled this code.....P0442 - Evaporative Emission (EVAP) System Small Leak Detected
is this no big deal? Is this just detecting the gas vapors leaving. i cleared codes and light went away. Just first time i got the light and didnt like it...want to make sure its not anything else.

05-07-07, 02:45 PM
I'm not sure if it detected the pressure release as a leak or not, but I don't think you should have had any noticeable pressure come out. Before that much pressure built up, the EVAP system should have purged it I would think. I never notice any pressure release when I open my tank, regardless of the fuel level.

05-07-07, 02:50 PM
well after clearing the codes it hasn't returned yet. It was a loud exhaust of gases when that cap came off. I mean loud in terms of opening the gas cap. as if you built up pressure in your mouth the pushed it out your lips. only way I can describe it.

05-07-07, 04:57 PM
I have a sneaking suspicion that the fuel tank is pressurized while the engine is running, which is why the owner's manual says to shut down when refueling, crack the cap, and, when the hissing stops, open the tank. Running, you would probably set a code. Just a guess...hence the recalls for fuel tank pressure sensor malfunctions.......That primary fuel pump in an injection system supplies a positive fuel pressure head, and you don't want fuel pump cavitation under any circumstances......Imagine what would happen if the engine went lean at 5500 rpm, WOT......

05-07-07, 05:34 PM
well i assumed it was due to the low amount of fuel and the pressure built up in the tank and didnt even think about it setting a code when fueling. Now that I think about it it makes sense that it would think its a leak in the EVAP. I mean it doesn't know that Im at a gas station and cracking the cap open.
Hopefully not something else and Iam rationalizing it into something simple.
Thanks for the replies guys.

05-08-07, 05:54 AM
The EVAP test enable criteria are much too strict to allow the test to run sitting at idle randomly.
You could have caught it at the end of a diagnostic cycle but it is doubtful.

Most EVAP tests are run while you are cruising on the highway.
It requires a general fuel level and a specific set of engine operating conditions. There are a few tests that it will run when the key is off depending on the year.
It is more likely a coincidence.

Pressure escaping from the tank is normal. Sometimes it is air going into the tank as it can be under a partial vacuum, but when the engine runs it constantly churns and warms the fuel. This can cause the tank to "pressurize" and is nothing out of the ordinary.

Here are the enable criteria for P0442 for an '04 Deville.

• DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1106, P1107, P1112, P1114, P1115, P1121, P1122 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).

Most of the time codes that set during fueling are related to the fuel level sensor. If you fill with the engine running or the key on the computer knows that the fuel level should not increase as there are laws that require the engine to be off during fueling (at least I am pretty sure it is a law).

At any rate, it is much more likely that you didn't quite get the cap on right on a previous fueling. 442 is a small leak code anyway.
I wouldn't worry about it coming back, but if it does it will require more testing.

05-08-07, 07:52 AM
thanks Will....
I'll let you know if it pops back up....