I just paid $110 for a mechanic to tell me my gas cap was loose!

I have a 2002 Toyota Tacoma with close to 97,000 miles on it. The other day the Check Engine Light came on, so I took it into the Dealer Service Center. They said it would be $110 dollars to run the diagnostics, to be applied towards any repairs that would be needed. Two hours later they call to tell me the error code was in the evaporative(?) system, They ran checks on whatever one checks, and everything was okay, so “it was probably a loose gas cap”. They said they tightened the gas cap, reset the codes and drove it to make sure the light didn’t come on again. Now I can’t really begrudge them the $110, because they did have to run all of the tests to make sure it wasn’t something serious, but it does bring up some questions. If this were to happen again in the future, how safe is it to just double check the gas cap and keep driving? Which raises other questions. How long would it take to know if this really was the problem and it is fixed? (Assuming the cap was left loose at the last fill-up, it took about 10 days and a quarter tank of gas before the problem was even detected.) Will the CEL turn itself off, or does it have to be reset somehow? Basically, if I tighten the gas cap will I get enough feedback to know that was indeed the problem, and how much leeway do I have (hours?, days?) before I know it worked or that I should go ahead and have it checked out?

The next time the light comes on just drive it into an auto parts chain store. They will pull error codes out of it for free. (This is not “diagnostic” work - but the error codes are called “diagnostic trouble codes” (DTCs).

Write down the exact codes (they look like “P1234”) and post them here.

If the light just stays on steady nothing disastrous is going to happen. If it starts flashing, don’t keep driving.

If a problem that set the CEL is fixed it will turn itself off after a certain number of drive cycles. (I.e. not right away but after a little while). The auto parts people can also use the code scanner to reset it.

If this were to happen again in the future, how safe is it to just double check the gas cap and keep driving? …Turning the fuel cap to tighten it is not dangerous. The next time this happens, check the fuel cap.

You’re Not Alone. And It’s Not Just Toyota. Your Experience Is Repeated Everyday By Owners Of All Sorts Of Vehicles, All Across The Country.

Cigroller Has Given You Some Good Advice.
If you don’t want to be dependent on the dealer who charges $110 to read your codes or inconvenienced by going to an auto parts store to get it done for free, next time consider purchasing a simple, inexpensive code reader. For example, an Actron Pocket Scan (about $50 at Sears or other brands available at auto parts stores) can read codes and turn off your light for you. It comes with a book that translates the codes (100s of codes that will usually need further explanation).
Link to some codes translated:
http://www.obd-codes.com/trouble_codes/ (Open this and scroll down the page.)

Also, as Cigroller said, “Write down the exact codes (they look like “P1234”) and post them here.” Keep in mind that the codes are only clues to which system in the vehicle has detected something out of the ordinary and that usually requires further diagnosis. In the case of a “major EVAP leak,” the first thing that should be tried is tightening the gas cap and then replacing the cap if that doesn’t work. Most issues are not as simple as a loose gas cap.

I usually check for codes, write them down, turn off the light, look up the code and do some reserch, while waiting to see if or when the “Check Engine” light and code(s) return in the near future. Sometimes you’ll then get additional codes that help zero in on the fault. Sometimes the light and codes never come back, as could be the case with a loose gas cap.

P.S. $110 probably isn’t too expensive if they actually checked and did further diagnoses. Some shops would charge $70 to $120 to read the codes and additional labor to check it.

Your car probably had a code PO455. See what “possible solutions” you could have tried had you read the codes at the store or home.


In addition to the good advice already given, I want to add that a steadily illuminated Check Engine Light (CEL) is really not an emergency situation, and it actually falls into the “check it and fix it at the earliest convenient opportunity” category. On the other hand, if your CEL is flashing/blinking, that IS tantamount to an emergency. A flashing/blinking CEL indicates that a misfire condition is taking place in one or more cylinders, and it must be rectified immediately in order to prevent very expensive damage to the engine and/or the catalytic converter.

But, I also want to respond to the OP’s question, “how safe is it to just double check the gas cap and keep driving?” Not only is doing this safe, it is really what needs to be done as the first order of business. However, it is so easy to properly secure a gas filler cap that I am mystified by how often people seem to run into this type of problem. I would say that, when you consider all of the tasks that one might have to do in a day, properly tightening a gas filler cap is perhaps the easiest one.

If the check engine light is not flashing and no odd symptoms give it a week or so to settle. And yes check the gas cap.

If still on get it checked out at your next convenience. A regular independent mechanic will sometimes check out your codes for free/quickly if you develop a relationship. I am lucky my 07 Acura MDX actually displays the codes in the Navigation.

Yes, andrew_j. There are great benefit$ for establishing a professional rapport with a good mechanic. In the mean time, getting the codes from McParts stores and posting to a forum such as this could save quite a bit of money. However, when the loose cap, or any malfunction, trips the CEL it will remain on for many days and miles even though the cap or other problem is taken care of. Correcting the problem will not turn the CEL off. Disconnecting the battery will not turn the CEL off.

“it took about 10 days and a quarter tank of gas before the problem was even detected”

That’s because the evaporative system does not get tested if the tank is near full.

conversely ;
Today’s customer got towed in,
rough running, won’t stay running, assuming fuel pump or the freshly full tank of possibly bad gas.
parts and labor and towing about $600.

After running the needed tests the tech ;
Removed the bent up air filter and cleaned the bugs out of the air flow sensor.
correctly put in a new air filter.
about $90. ( yes there’s a shop minimum for diag. )

Sometimes you get a pleasant surprize after assuming the worst.

Ignorance can be very expensive…CEL’s are profit centers.

I don’t think anyone has addressed one of your questions. It could take several days depending on your driving habits for the CEL to come back on even if the problem wasn’t corrected. The light wouldn’t likely come back on in a short test drive the mechanic would have done after tightening the gas cap. The ECU has to recognize the fault multiple times before turning on the CEL.

I’d also suggest buying a code reader for your own use. Just a cheap model will give you the code number and is all most car owners need. I think you can pick up a cheap model on ebay for under $50.

“That’s because the evaporative system does not get tested if the tank is near full.”

Thats not my experience, nor others who have posted here that their check engine light came on right after fill up with a code for the evap system.

One common problem with the evap system occurs when drivers chronically overfill the gas tank, but that trips the light shortly after the fill up, usually the second time the vehicle is started. Since yours did not come on until ten days later, I guess that you are not the type who always tries to get the last drop into the tank.

Good news is, if you find the cap is loose and tighten it, the light should go off after three drive cycles. The code will remain for up to 30 drive cycles in the history memory of the computer. Remember, three clicks to tighten the cap and always stop filling the first time the pump handle clicks off, do not top off the tank.

Thanks to everyone. Your answers have been very helpful, just what I was looking for.