Tip & How-To about Buick LeSabre

Gas Cap Loose Service Engine Soon Light On

This can happen if the gas cap is not properly installed. Make sure you hear several clicks when installing. After 10 or so starts the Service Engine Soon light usually goes away.

A second cause could be a problem with the ground wire that comes from the gas cap sensor and goes to the body. Look up into the wheel well by the filler pipe to check.

A third can be the result of a vacuum leak in the fuel evaporator (EVAP) system. Look for any hoses that go from the air intake to a sensor on the fuel rail (fuel injected cars). Many cars have plastic engine covers that have to be removed to see the fuel rails, sensors and hoses. Most require unscrewing the oil filler to get the cover off. You may not think the hose is leaking but replacing may make your problem go away. A small vacuum leak can also affect the fuel flow and affect the engine operation.

My experience is with the 3.8 engine but this probably applies to lots of engines. On the 3.8 it is the two piece hose that comes from the air intake with one small hose going to the top of the engine and the other going across the front of the engine into a hose that does a 180 degree turn that comes back to a sensor. It costs about $25 and is a dealer item.

There may be other causes but these are three common ones.

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my service engine light came on, i went to get it reset and i thought the problem was solved. few days later the light came on again. i found out what the problem is my po442 emission vapor control systemon my truck.how do you fix the problem? and where do i start?

Usually a vapor control fault is caused by not putting the gas cap on straight, or by a leaking gas cap. This car is 10 years old, so you may have a leaking gas cap.
Also check for damage to the neck of the gas filler such as might happen if someone drove off with the nozzle still in the car, but neither your spouse nor any of the kids will know anything about such an event (!) If the neck is not damaged and you are sure that you are putting the gas cap on properly, try a new cap.
On most cars, this code will reset itself after a few start cycles if the problem is fixed, so you should not need to take it anywhere to get the light reset if you solve the problem.

Jan 23, 2011 | 2001 Chevrolet S-10

2 Answers


Most likely an evap system fault code stored in engine computer. Best bet and cheapest thing is go to the dealer and buy a new cap. Install the cap and drive the car for a few days if the light goes off, your all set, if not you need to check for codes. Then probably find a leak or a faulty evap vent valve or purge valve.

Oct 07, 2010 | 2001 Pontiac Bonneville

1 Answer

service engine soon light came on. AutoZone read

Sometimes you have to wait a week for the light to go off, the computer has to go through several start/run/stop cycles.

Nov 22, 2009 | 2004 Oldsmobile Alero

1 Answer

service engine soon light came on after full tune-up

Make sure the gas cap is on tightly. A loose or faulty gas cap can cause an intermittent check engine light. Hope this helped and best wishes.

Aug 18, 2009 | 1995 Chevrolet S-10 CA Edition

2 Answers

evap leak in fuel

Remove the gas cap and re-install it making sure that you hear it click several times. What your evap leak could be is the gas cap allowing gas fumes to escape. All it takes is a .040 leak to turn on the engine light. If it persists you'll have to have the emission system smoke tested. What happens is the system is literally filled with smoke and the leak will be found by where the smoke comes from.

Nov 23, 2008 | 1998 Buick Century

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