97 Sentra, Check Engine Light: P0440, P0446

Jun 18th, 2003, 09:36 PM

Check Engine Light goes on shortly everytime after I add #87 gas. It went off after I added #91 last time, but came back again after #89 gas this time.

Checked the codes: P0440(Evaporative Emission Control System Malfunction) and P0446(Evaporative Emission Control System Vent Control Circuit Malfunction).

What can I do to this probelm? Have to use Premium gas all the time? or there is some problem with this car?
It's a 1997 Nissan Sentra GXE, 82K miles.
Thanks!

Nostrodomas · Jun 18th, 2003, 09:53 PM

Yea its gonna be a problem once you go to get your car smoged. The evap system is a pita. I just ended up taking it to the dealership.
But other than that, it wont cause harm to your car, just to the air.

Jun 19th, 2003, 11:51 PM

50% of the time all you need is a new gas cap....

)

AnthMC · Jul 11th, 2003, 11:54 AM

Sometimes it is the gas cap and it could also be the sensor under the hook, thinking you taking in more air than you should. My friend has a 98 200sx and has had his engine light on for well over a year and half lol, but he took the bottom of his air filter off..... Don't ask why and its just running the engine to the ground... oh well some people just don't appriate hahaha. I haven't ever had my light on in my '99 Sentra even after a few mods.

Jul 13th, 2003, 10:53 PM

I've had the same trouble codes. Still got my light on. While back I dropped my gas cap while fillin up. It was after that I started getting these problems. Think that's the cause?

Ninety-Nine SE-L · Jul 14th, 2003, 05:34 AM

true, try a new gas cap first. The gas cap must make a proper seal or else you're releasing unburnt fumes. When you remove your gas cap, do you hear alot of pressure release from the tank?

Jul 14th, 2003, 05:43 PM

Yes. When I unscrew my gas cap I can hear alot of presure release. Good or bad?

Ninety-Nine SE-L · Jul 14th, 2003, 07:09 PM

good. The fuel in the tank naturally vaporizes into a gas within the tank. Since unburnt fumes are more harmful to the atmosphere than burnt fumes, the car has an EVAP system. The Evap system periodically purges the tank of the fumes and empties it into the intake manifold so it can be burnt.

If the gas cap is bad, the fumes will leak out of the tank full time. This means the pressure cannot build up and the EVAP is sensing that there is nothing to purge from the tank.

Any properly sealed fuel tank will have built up pressure inside. So when you open the gas cap, there should be a big pressure release. If there is no pressure release when you open the cap, chances are, there is a leak in the tank (most likely a bad cap)