Foo - Engine Light Interpretation

On my wife's '99 Town Car, the engine light came on one day, about a year or so ago. We had it scanned and it was a "major emissions leak." I was told this really means "gas cap." Well, taking the cap off and putting it back on didn't help, so I bought a new gas cap and the engine code was cleared and it stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

You get the point. What else could "major emissions leak" mean, and why does it take a week for the engine light to come back on again? Why doesn't the light just come back on right away once it's cleared?

As far as gas mileage, my wife has lost about 1.5-2mpg average (based on the very trustworthy :rolleyes: dashboard information center) since this has started happening, so I feel like there may actually be a problem here...

Thoughts?

ETA: I just thought of something. Before this started happening, the intake manifold was replaced and I never trusted the work. I can't remember the exact timing of the manifold repair vs. the engine light first coming on, but I wonder if the two are related or just coincidence. Maybe something wasn't hooked back up correctly... but I am not sure what I would look for.

http://www.youfixcars.com/gas-cap-code.html

too many...?
http://engrishfunny.files.wordpress.com/2009/11/engrish-funny-brackfas-burritos.jpg

wonder if there couldn't be a small leak in the conecting hoses between the cap and the tank? eleven year old rubber may have deteriorated over time.

Try Googling "Lincoln Towncar forum" and join the forum that pops up that looks the most busy. Most cars have a following and the motorheads who hang out at those forums can often diagnose problems much more quickly that certified dealer mechanics. I've gotten great answers from Ford Taurus, Ford Escort and Hyundai Elantra forums. They have nothing to gain, except that they tend to take a personal pride in the car the drive and want others driving the same model to have a good experience, so the advice is generally quite good.

I would call Ruben.

I would call Ruben.

Rubens Car Talk tm

"no talent?no tools?no problem-o!"

This is an easy fix. Put a small piece of electrical tape over the light.

I suggest you bring it to your local dealership :lol:

and why does it take a week for the engine light to come back on againWhen you clear the codes it takes a certain amount of time (running hours) before the codes are re-populated. In other words, you have never fixed your actual issue. Get the actual code, you can look it up for your model vehicle and go from there. Autozone and other auto part stores will read the code and clear it for you for free.

Most likely a vacuum hose or two or all of them are cracked and leaking, needing replacement.

The code goes away and comes back because the computer has to see so many running hours of the condition before it trips it.

if it was a nissan, I could easily tell you that "service engine" really means "sensor is broken"

O2 sensor possibly. Not sure but most cars I have dealt with have a sensor in the manifold. From my experiences cel's (check engine lights) are usually just some emissions thing going goofy. I know my impreza hated the new exhaust till I reflashed the cpu. I think autozone will do a free engine scan. Again assuming you have and obd2 plug in the car.

OBD-II should tell you specifically if it's the front or rear O2-sensor that's out. There are adapters that connect a Palm Pilot or iPhone to ODB-II system, but not really worth it for backyard mechanic.

Most problems of this sort are near the fuel-filler neck. Overflow hoses or roll-over valves can become defective over time. One very common issue is the filler-neck gets distorted by hanging heavy fuel-nozzles on them. Or even worse, people who push down heavily on the fuel-nozzle. This ends up ovalizing and distorting the outside surface and the cap won't seal well. You should always hear that vacuum sucking sound when you undo the cap to refill. If not, there's a problem in that area.

if it was a nissan, I could easily tell you that "service engine" really means "sensor is broken"

I have half a suspicion this is the issue.

Only half a suspicion because there's a lot of things it could be. However, it's entirely possible that during the manifold replacement they damaged the wire to the ECU and so the connection is intermittent.

Also, there's some useful information in the link StupidlyBrave posted above.

I would call Ruben.

Smart choice my friend.

OP... if you were nearby, I'll tell you to drive by and let's scan that baby (oh yeah, I have my own OBD-code-thingy scanner). With the actual code, or codes, we could go to a few websites online an get info about different people that had the same code and what it turned out to be.

Saying it must be the gas cap was a very cheap answer from your mechanic. I could be many many things. Maybe the gas cap is "usually" the cause for that specific code. But there might be more.

I really recommend googling the actual code rather than the description associated to it. Different scanners associate different descriptions to the real codes.

One great place to start researching code stuff is a link I found on "Eric The Car Guy (http://www.ericthecarguy.com/)" website. Go to the "codes" page and check it out.

Also keep in mind that when cleared, the code doesn't really "go away". The car's computer has to see it for an x amount of time/miles before triggering it. Otherwise you will have check engine light flashing all the time with false alarms.

EDIT:

After reading Dany's post I remember something else. Get the full list of codes that your specific car can spit out (haynes manual?) . Many things/sensors have specific codes. You can rule out those components if their codes are not showing up.

You're probably putting the cap on tight enough right? It's supposed to snap a few times. We do that pretty religiously now but it doesn't help keep the light off. I have a usb cable so I can plug the laptop into the car and clear the code myself but it pops back up again anyway.

On my wife's '99 Town Car, the engine light came on one day, about a year or so ago. We had it scanned and it was a "major emissions leak." I was told this really means "gas cap." Well, taking the cap off and putting it back on didn't help, so I bought a new gas cap and the engine code was cleared and it stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

About a week later, the light came back on. Code was scanned, same issue, code was cleared and stayed cleared.

You get the point. What else could "major emissions leak" mean, and why does it take a week for the engine light to come back on again? Why doesn't the light just come back on right away once it's cleared?

As far as gas mileage, my wife has lost about 1.5-2mpg average (based on the very trustworthy :rolleyes: dashboard information center) since this has started happening, so I feel like there may actually be a problem here...

Thoughts?

My dad had the same exact problem and the dealer was nickle and dimin' him to death. Till one day (I think the third time we took it in) the mechanic pulled my dad to the side and told him all he had to do was to be sure to turn the gas cap three times every time he got gas or takes the gas cap of for any reason. He did this and the check engine light never came back on. It was that simple!

My dad had the same exact problem and the dealer was nickle and dimin' him to death. Till one day (I think the third time we took it in) the mechanic pulled my dad to the side and told him all he had to do was to be sure to turn the gas cap three times every time he got gas or takes the gas cap of for any reason. He did this and the check engine light never came back on. It was that simple!
Ya, we have been doing that, but it still comes on. I am sure there is some other leak somewhere, but I just need time to test things out.

You should always hear that vacuum sucking sound when you undo the cap to refill.

Presumably, after a weeks time, you have burned off some amount of volume in the tank. So you should hear that sound. This may also explain why the sensor kicks off again after a week.

Presumably, after a weeks time, you have burned off some amount of volume in the tank. So you should hear that sound. This may also explain why the sensor kicks off again after a week.

The only sensor in the gas-tank is the fuel-level sender. And I'm assuming it's reading the proper fuel-level and sending it to the gas-gauge.

Something just popped back into my head seeing as this is a Lincoln. Ford had major issues with O2-sensors getting contaminated with silicone from various gaskets. They apparently used too much of it in some areas and it got through the engine into the exhaust and killed the O2-sensor. As RubenX mentioned, find the specific codes flagged and look them up for your specific car/model. A bad O2-sensor might be mis-interpreted as a "massive emissions leak", depending upon which scanner you're using.

Shot in the dark-02 sensor?

Also, OBD readers are great to have. Mmmm tools...:D