Question about 2004 Pontiac Grand Prix

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Computer is saying check gas cap - 2004 Pontiac Grand Prix

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Actually what the computer is saying is first check the gas cap. If its on tight and the rubbler seal is in good shape and the sealing surface on the filler neck is good then decide if you want to replace the gas cap which is the cheapest route if the seal is pancaked enough that it doesnt seal anymore. Then drive for a few days. If this fixed the problem then the light will reset itself after a couple cold starts that allowed the system to be tested again. If this didnt work then the car need s to be put in the shop for diagnosing. You could have a bad solenoid of vacuum leak somewhere.

Posted on Jul 14, 2009


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Posted on Jan 02, 2017


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Why does the check engine light comes on saying the gas cap is loose or off when it is on tight.

looks like there is a sensor on the filler cap/lid side.
which is faulty and not sending correct signal to the main computer in the car.

Apr 29, 2017 | 2006 Kia Rio

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Check engline light on and check gas cap message

If the gas cap is tight then rpelace it.

May 24, 2012 | 2005 Buick LaCrosse

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The onboard dash computer of my 2006 sierra z 71 4x4 says to tighten my fuel cap, and now my check engine light is on. there is only 94000 km on this truck

This is a common issues with this truck. You have probably tightened the gas cap a bunch of times and are like what the heck. The gas cap DIC warning is part of the evaporative system to reclaim gas vapors. The onboard computer on the truck monitors the gas tank vapor pressure, which checks for vapor leaks in the fuel system. This warning involves a pressure mismatch, which the onboard computer relates to a fuel vapor leak. It assumes fuel vapors are escaping via your gas cap thus circumventing the purpose of the evaporative system. A common fix is to dip your finger in a bit of motor oil and put it onto the gas cap gasket to seal it (like you do an oil filter.) This should solve your problem. If the gasket is ripped or torn then buy a new gasket or a new gas cap. The reason for the oil is to lubricated the gasket again as they get very dry over time, given their location.
Regards, Tony

Apr 20, 2011 | 2006 GMC Sierra

1 Answer

Yellow warning light that says check is on What does it want? In manual it says take to dealer

Take it to a Pep boys if you don"t have a code reader.
They will check out the computer code warning you are getting right noe.
The cost will be about $40 or 50 bucks.
The dealer will charge you three times that much,plus Pep boys will give you a up front free estimate if you need any repairs.
Bet it's the gas cap though.
Try tightening your gas cap and driving the car around far a hundred miles or so.
remember never put gas or loosen the gas cap when the engine is on.
The computer will pick up the venting like it would a leak,thus sending a warning code to the computer.

Nov 25, 2010 | 2005 Toyota Corolla

1 Answer

On the handheld computer diagnostic too, it readout says P0174, which is defined as "OBD II P0174 Fuel System Too Lean (Bank 2)". What kind of repair am I looking at?

Check or replace your gas cap. When a gas cap gets old it can no longer hold pressure in the tank causing gas fumes to leak out and ambient air to get into causing the check enging light reading. Try replacing it first. It'll only cost you $15.00. Reset your computer with your hand held device. It takes 50 miles for the computer to reset itself. If the problem does not come back after 50 miles then you've got it done cheaply. Good luck.

Sep 19, 2010 | 2002 Mazda MPV

1 Answer

Check engine light comes on have had it in twice for a fix/they say its the gas cap well the first time they cleaned the old cap and re set the computer.the second time they replace the cap and re set the...

Well, I would check the filler neck connections and the condition of the filler neck. If this is leaking there, or the tank is leaking, the loose gas cap code will show up.

Keep taking it back to the original shop until the problem is fixed. Have faith.

Jul 05, 2010 | 2004 Toyota Avalon

2 Answers

My check engine light came on. The dealership said "filler neck leaking causing evaporative leak." The gas cap also says "loose cap will turn on check engine light." Would like to try a new gas cap but...

sad to say sir that how to clear the code is not easy in manual clearing, you need diagnostic tool to clear the dtc, but some dtc will cleared by 20-50 consecutive warm up if no other trouble code detected by the computer

Jun 19, 2010 | 2001 Chrysler Town & Country

1 Answer

Check engine light is on, hooked up computer to brain and it says it was a fuel leak sensor or fuel leak evape sensor. where is this sensor located, it also only shows fuel gauge reading of 3/4 tank full...

check ur gas cap first for proper seal and or not tightened this is the usual problem the evap system is from your fuel gas cap [gas--vent lines /gas tank-evap canister-throttle body] to ur throttle body/injectors if gas cap good need to check the lines and components for a leak disconnected /cracked broken-as well as the sensors and canister

Feb 21, 2010 | 1992 Ford Ranger

2 Answers

Check engine light on says check gas cap. Is it the cap or a sensor?

The evaporative emissions system uses a vaccuum pump to check the fuel system to make sure that fuel vapors cannot escape into the atmosphere. If you leave fuel cap loose the computer will detect it and set a computer code and turn on the check engine light. If the cap is tight and the light still comes on, you may have other problems. Hopefully your vehicle is still under warranty, as evaporative emission system leaks can be very difficult to locate and repair, even for the dealership mechanics.

Aug 28, 2009 | Chevrolet Cobalt Cars & Trucks

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