amge

Well I got a check engine light on my wife's 99 Civic EX. We took it to the three different dealers and all three say that it's reading a fail error. Code 999. So they just reset the ECU and it's fine until we get low on gas. Then the check engine light comes back on.

We changed the gas cap, and had the fuel filter replaced.

Anyone heard anything like this? Any tips?

Yeah go ahead and say, sell the car. But how am I going to sell it with the check engine light on?

BTAC Type-S

Sometimes you need to drive around for a few days after changing the gas cap for the CEL to go away. Also, make sure you tighten it at least three clicks. Again, wait a couple of days. Resetting the ECU should help as well. Do you have any aftermarket parts on the car?

teflonian

I had a similar problem on my brother's car. His was a 2001 Chevy Cavalier. They finally had to replace some part that was responsible for detecting the deficiency/eficiency in the fuel system. It took them four or five trys where we had to take it bake to the dealer. Thankfully we were under warrranty. Good luck...!

amge

Thanks for the tips.

We are waiting to refuel the gas two or three times before we take it back to the dealer.

I thought it might have something to do with the fuel system.

otter

If nothing else seems wrong, outside of the light being on, it could just be a bad sensor.

Vortex22

Possibly a bad O2 sensor or faulty emissions equipment.
I gaurantee that it has something to do with emissions, It's perfectly safe to drive.

FastShark85

Ditto on the O2 sensor. Your car sounds like it's the right age for the sensor to give up the ghost or trigger the warning. Just a possibility.

amge

Do you know if it is ok to take it out and try to clean it myself?

Or is it all enclosed? Because the O2 sensor is on the air intake tube right?

Well this check engine light came on after we drove from San Diego to Las Vegas. When we changed the air filter, and it was black as night. So may be that is it.

FastShark85

The O2 sensor should be somewhere AFTER the air intake. It tells the car's computer whether the gas/air mixture is too lean or too rich.

My 02 sensor is mounted to the part of the exhaust housing the catalytic converter. Try locating a Honda Civic forum. There's tons out there and they could tell you the answer you're seeking within minutes.

I don't think cleaning an 02 sensor does anything but make it clean. New O2 sensors for a Civic should be cheap and easy to find at a local store.

inbeastic

Make sure you tighten your gas cap like crazy. (more than 3 clicks) If you dont't the engine light comes on and you have to take it to the dealer to reset it.

onetime2

Could also be bad gas. If you are consistently using the same gas station it could be them. If you are, switch stations for a while and see if it stays off after it's been reset.

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shakran

"I gaurantee that it has something to do with emissions, It's perfectly safe to drive."

sure it's safe to drive but it'll be a pig. Most CEL's on hondas send the system into closed-loop mode, which means default cold-start settings. You'll use gas like a mother. You'll need to figure it out. FYI I have never heard of bad gas causing a CEL. I have also never heard of a code 999 on ANY honda.

DEI37

The primary reason bad gas COULD cause a CEL is if it were watered down, or was just bad to where it caused a misfire. Today's computers will catch that, and set a random misfire code. Otherwise, shakran, I believe you to be correct. I haven't heard of it, either, just that is about the only reason I can think of.
And, I know NOTHING about Honda, so I won't comment on a code 999.

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onetime2

The reason bad gas can cause this is the crap that is floating in it. Whether that crap is water or more likely sediment from the storage tank. Gas stations are actually not supposed to pump gas for a certain number of hours after a fuel delivery but none adhere to it. The reason is all the crap that gets stirred up when the delivery takes place. When that crap gets either burned up in your engine or it passes through the exhaust ports without being burned the sensor gets confused and codes.

Sion

amge, I tried to google your trouble code 999, but was unable to find anything specific to your Honda. the only thing I found was a generic code that referred to shift solenoids, which has nothing to do with your problem.

but, from what I know of OBD II (on board diagnostics II - 96 and newer vehicles) and what the dealers told you, Id have to ask this question:

are you sure you said that right? they told you "reading a fail error" and not something like "failure to read error"?

I ask this because OBD II is a much more specific system than the original OBD system was. in most cases, a trouble code will target a specific vehicle system. (for example, say that code 124 means that your O2 sensor is giving out of range readings, the code message is usually something along the lines of "Oxygen sensor circuit out of range".)

also, I would not have left the dealership until I was satisfied with the answer they gave me. I would have kept on asking questions until I understood them. Make them keep explaining it until either you understand it or they just flat out admit that they dont know. THEN move on.

finally, if the vehicle is under warranty, insist that they find the problem. if the CEL is coming on, that means a problem exists, either with the car or with the diagnostic system itself. either way, they are obligated to figure out the problem and if it is covered by the warranty, fix it.


now, on to the problem itself. some questions that could help diagnose it.

how low on gas do you have to be before the light comes on?
does it stay on continually or just flash at you occasionally?
does the vehicle have one of those "Low fuel" warning lights (or audio tone) that comes on when the gas level gets too low? does it still come on? does it come on at the same time as the CEL?
has there been any change in the vehicle's performance? sluggishness, hard starting, etc?

my wild ass guess, based on the limited info I have, would be that the low fuel sensor has failed, thus turning on the CEL.

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Peryn

First off, was it black from dirt, or was it oily. If its oily, you got something else going on. Chances are, your PCV is plugged, and oil and air is going out the wrong way from the engine into your air filter. That will start to build up and restrict ariflow, killing performace, possibly throwing a code. PCV are cheap and easy to fix too

skippy

Yeah what he said too

forumguy

Thanks for the great advice everybody. Very helpful!

amge

Wow several days with out checking the forum and I got more responses. Thanks again for everyone's input.

Well according to the dealer he said it was a "False Error Code" I'm pretty sure he said it was 999. I looked on the internet too for OBD codes and I didn't see 999 either. Oh and for this car it was the older OBD not OBD II. Also it's not under warranty any more so we have to pay for the diagnostics.

Gas milages still seems the same. And there has been no performance loss at all. They changed the fuel filter, and reset the computer. The CEL was out until the gas tank was getting near empty. As soon as the low fuel light came on the CEL light came on and it's back again.

Now I'm thinking it's the sensor for the low fuel. So I think we will try that next.

Oh and the air filter was black from the dust and dirt, not oil.

Thanks again for the input.