Check Engine Light says Gas cap not on correctly? Huh?

I have a 1997 Dodge 1500 with at 318 V-8 engine. The Check Engine light came on the other day so I took it to a local parts store to run a diagnostic. The report said my gas cap was not on correctly and something else I cannot remember at the moment. So I went and checked the gas cap and everything seemed to be fine. Any suggestions?

Get a new gas cap. Yours probably has a bad gasket or a crack. Or, you could have a cracked hose in the Evaporate Emissions control system, which is a pain…

If your CEL came on and it turned out to be the gas cap, you got off easy.

If the gas cap does not seal properly, it will trigger the Check Engine Light. It’s an emission control thing. Can’t have that miniscule amount of VOC’s leaking into the atmosphere .

If you reseated the cap, reset the system and there is no further occurance, fine. If the light reappears, replace the gas cap.

I emphasize that you got off easy if the gas cap is all it is. The CEL is a gold mine for auto repair shops. There is even a local radio commercial for a transmission shop that says if your CEL comes on you should take it to them for a transmission diagnostic.

Imagine the soaking you would get if you did that.

I normally take any of my vehicles to a place like Auto Zone or some place similar that runs a free diagnostic. When they gave me the report of what my error could be I kind of brushed it off. A gas cap does not seem to be a crucial part that cannot wait.

In many ways I hate the CEL because of some of the small stuff that triggers it. It makes me miss my old truck that didn’t have it.

I’m not sure if the '97 model Dodges have this feature (I drove a '99 before buying my '03) but at least in 3rd Generation Dodge Ram trucks, you can avoid having to go to anyone for a diagnostic when the CEL comes on. It’s called the “key trick.”

Insert your key into the ignition. While holding down the trip odometer reset button, turn the key to the on position (not the start position, but where the gauges, lights, and radio come on) and then off three times, fairly rapidly. On-off, on-off, on-off.

The odometer will then display the error code. I’ve had the gas cap error several times when I just didn’t tighten it down enough, and IIRC, that code is P002.

Once you have the code, you can find its meaning online. P002 is a small leak in the evap system; I believe P003 is a larger leak, sometimes associated with the cat. converter.

Still, it’s nice to be able to go to the shop knowing what error the computer is throwing. I generally keep mum about it, and wait to see if the garage is honest.

The kind of diag tool they use at a parts store is very generic. A 97 BR body wouldn’t monitor the fuel system pressure. You need an accurate diag tool or at least a competent technician or maybe both to figure out what is wrong. If I had to hazard a guess, knowing this vehicle fairly well, I would say the purge solenoid is clogged with carbon and needs to be replaced. You can pull the lines from it and check it easily. The code for it would be similar to the one for the gas cap.

OK, what is this and where is it at?

There are a bunch of things that can trigger a leak code. A loose gas cap is probably the most common, and most likely. But and this is a huge but there are many other things that can trigger the same code.

I’ll just mention in passing that even retightening the gas cap doesn’t cause the CEL to go off in some cars, notably mine (Mazda minivan). You have to go to the dealership or a garage to get it turned off. I find that extremely irritating.

It’s on a bracket on the side of the intake manifold. It has a 2 wire plug and 2 vacuum lines aprox. 3/8 diameter on it. The lines run back to the charcoal canister by the fuel tank. Pull the vacuum lines off and see if charcoal is present. If so the solenoid needs to be replaced and the vacuum lines need to be blown out with an air hose, changing the vapor cannister isn’t a bad idea either, but were still guessing so take it with a grain of salt. You will need to disconnect the lines at the canister to blow them out. Good luck.

The PA annual emission test (only in selected counties) involves connecting the fuel cap to the testing apparatus via an adaptor which pulls vacuum on the cap. Failure of the cap, and/or presence of a CEL at time of inspection and/or missing/modified components = fail.
The above only covers vehicles from certain counties of registry which get a visual inspection and cap check. In other counties, tailpipe and dyno are involved.

“Gas cap” is pretty common, and it means you just didn’t tighten the gas cap fully last fill-up; most of the time.

The Service Engine Soon light on my 2003 Altima came and from my research online I figured it was the gas cap, but since that didn’t seem to clear up the problem I took it to a local mechanic. They ran some diagnotics, but recommended that I take it to the dealer so they can clear the light and run the diagnostic test that was designed for my car. It ended being the $800 catalytic converter-- fortunately it was still under warranty at the time.

Granted that was a Nissan, but it was a similar situation…

I changed the air filter in my 2005 Ford Freestar the other day and in the process, had to disconnect a sensor on the hose that runs between the air cleaner and the intake. I forgot to reconnect it before I started the car and it threw up a code. Reconnecting the sensor didn’t turn off the CEL and I had to take it to a friend of mine to get it turned off. Fortunately I knew someone with diagnostic equipment.

One thing he told me is if you disconnect the battery for 3 or 4 hours, the codes will all reset, so if you have a temporary code, you can shut off the CEL like that.

The Car Talk guys addressed this very issue a couple of weeks ago. Their suggestion when the CEL keeps coming on was to put black electrical tape over it.

Christ did they really? :rolleyes: Assholes.

I know. :rolleyes: Answers like that make all their info very suspect. :dubious:

:eek: Whoa, easy there! I thought it was obvious, but I’ll clarify that they were joking! After the black tape, they gave the real answer (this is something you need to get taken care of, take it to a mechanic). I guess I shouldn’t assume that everyone is familiar with their humor.

If you haven’t heard their show I highly recommend it. They know a TON about cars and are entertaining as hell.

I don’t listen to them, because every time I do, I wind up screaming at the radio, NO you ignorant slut that isn’t how it works, CITE.
IMNSHO they are a couple of guys that own a shop, that are sometimes sorta funny. They are not overly bright, or well versed on cars.
I’m sure they mean well, but frankly they aren’t all that sharp, and they never let the facts get in the way of a joke no matter how lame it might be.
They are entertainment, no auto repair.

So you were whooshing us, right? :rolleyes: Something considered very rude in GQ.

Jokes aren’t so bad, but deliberately wrong answers are.