SES Light is on, AGAIN!!

I have a 2003, 2WD, 5.3l, Ext cab, I am the original owner. Next week will be my sixth trip and second dealership, because the check engine light is on again. It always reads as a fuel system error. I've been accused of not knowing how to put the fuel cap on,(VERY FRUSTRATING) the cap has been replaced, a sensor/valve has been replaced, who knows what next weeks visit will bring. Can anyone offer any suggestions that I may take to the service people at the dealership? Can anyone tell me how many clicks does it takes to properly seal a gas cap after refueling your truck? If it is just a matter of, tightening the gas cap, why doesn't the light go off the next time I start the truck? The geniuses at the dealerships can not answer these questions.

I believe the GM standard is at least 3 clicks. But if it is not sealed right the light will come on.

There may be a way to check to see if it is fuel cap related. My grandfather just bought an Chevy Astro and the light came on, so he took it to the dealership and they said it was because the fuel cap was not tight enough. They also said if it is the fuel cap then the SES light should not come on until the gas tank is past 1/2 empty. So, do you notice if it will come on only with the tank past 1/2 empty? If not, it may be something else.

Also, sometimes the computer may have to be reset to clear the trouble codes before the light goes off. To reset the computer you can let the dealership do it or disconnect the battery for about 5 min.

Thanks for the reply. This time I made sure to look at the gauge when it came on. It was two days after I filled the tank, 3/4's full. I hope they didn't design a system to be this sensitive, requiring a trip to the shop or pulling the battery cable just to reset the computer everytime the gas cap becomes a little loose.

I believe the GM standard is at least 3 clicks. But if it is not sealed right the light will come on.

There may be a way to check to see if it is fuel cap related. My grandfather just bought an Chevy Astro and the light came on, so he took it to the dealership and they said it was because the fuel cap was not tight enough. They also said if it is the fuel cap then the SES light should not come on until the gas tank is past 1/2 empty. So, do you notice if it will come on only with the tank past 1/2 empty? If not, it may be something else.

Also, sometimes the computer may have to be reset to clear the trouble codes before the light goes off. To reset the computer you can let the dealership do it or disconnect the battery for about 5 min.


For the first part in bold i say the dealership informed him incorrectly, I had a full tank and had the light come on for the same reason. I know this because i had it scanned. The second part in bold; Disconnecting the battery does not clear the codes 99 and up anymore, it sucks but that is the way it is. I think they did that because one tech told me that they used to get alot of people coming in complaining about the ses light coming on , but they disconnected the battery to see if that would "fix" the problem. Most times when the ses comes on , it is not something that can cause any real damage UNLESS the ses light is flashing which means a misfire and that if left too long can cause damage to the engine or the cat.

I had the same problem when my '03 was new. It turned out to be the evaporative canister. Replacing that solved it and I haven't had a problem since.

There are some misconceptions regard the operation of the OBDII system needing to be dispelled. First, the SES flashes only if the problem illuminating the light is present, and is an immediate threat to the convertor. The problem will need to be seen by the computer at least twice before the light stays on. There are two methods of extinguishing the light. One is to use a tool, which accesses the system, and provides a reset request. The other is for the system to fail to see a problem setting the code for the next twenty or more driving cycles where the test is performed and passes. The count for the automatic reset varies vehicle to vehicle and depends on the source of the problem. My experience with these systems is that they are very sensitive, prone to connection problems, and have been a source of constant aggravation since their inception. I have dealt with these problems as a driveability tech for nine years, and they continue to be a problem. Blaming the customer only aggravates the problem, and indicates a lack of understanding of the situation. If the gas cap threads onto the tank correctly, and clicks once it will ratchet, not tightening anymore. This system is built to be self checking, and does a poor job at best, and worse on some vehicles. Good luck, and have the dealership contact me if they cann ot get the system to correctly self check, or cannot find the problem. This is a dealership issue, not a GM issue. I have gotten nothing but help when I requested it. Ray

Hey Ray,
Thanks for the reply. Sounds as though you know your stuff. I'll take you up on you offer if they can't fix it this time. The truck is in the dealership as I write this. They are also replacing the driver seat back cover because it wore our prematurely. Sorry to say, the quality is just not there.
Thanks again,
Another Ray