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May 13, 2005 12:01 AM

Broken: Prius check engine light

Paul Schreiber has a problem with his Toyota Prius:

according to the dealer, i have to drive the car for at least 20 minutes 2-4 times for the car to believe the gas cap really is fixed.

stupid computer!

Read Paul's full entry.

Yes, he's already read the previous TIB post on the Honda CRV.


Hmph! On the Crowne Victorias we use the 'CEL' light is actually useful. Lets you know precisely when the gas tank is about to explode. Mind you that's not very useful when you go into the store for a pack of smokes and you asked Kreichek to wait in the car for you. Tends to give the bastard a running start if he notices it in time...

Posted by: W G B Spender at May 13, 2005 09:38 AM

Mistake 1: You went to the dealer. Avoid doing that if at all possible.

Mistake 2: Not knowing that the gas cap has to be on tight to prevent the check engine light from coming on. This has been necessary for years. At this period in time, it's mostly only chicks who aren't aware of this, and evidently a guy or three who drive Prius'.

Posted by: Dave at May 13, 2005 10:00 AM

Maybe this guy is really really really proud that he owns a Prius and wants to brag about it in every breath he takes. I had a friend in high school who bought an Ipod Mini the first week they came out and every little time he could, he broght up the mini. Check engine lights come on all the time. Unless they are flashing, it doesn't even phase me anymore. Then again, I do drive a 96 Grand Am four banger. Not that I'm bragging or anything.

Posted by: Jeff at May 13, 2005 10:22 AM

I had this problem once, it took the dealer 3 visits to figure it out. It was a selinoid (sp?) in the gas tank. They said it had something to do with the vapors in the tank setting off the CEL because the computer thought the vapors were escaping the tank.

Posted by: Alex at May 13, 2005 11:21 AM

I had the same thing happen in my VW Passat. The check engine light came on after I only had the car for 4 months. The mechanic told me it was probably the gas cap and that I could still drive it. I told him I had already checked it and the light was still on. Being it was still under warranty I took it in to the dealership and it turned out that my intake system was not sealed properly when it was manuafactured. The VW manufacturer is broken and so is your dealership!

Posted by: Chaos at May 13, 2005 12:33 PM

Chaos's story points out the dangers of overloading the check engine light to mean a gazillion different things that range from the mundane to the serious. A loose gas cap happens so often that is just assumed to be the reason and may cause people to ignore more serious problems.

Posted by: Carlos Gomez at May 13, 2005 12:53 PM

Why don't these car companys just make a light that says GAS CAP??? Then you know it is just your gas cap. CHECK ENGINE means to check your engine, not you gas cap.

Posted by: John at May 13, 2005 02:34 PM

Apparently, his Shift key is also broken.

Posted by: James Kew at May 13, 2005 02:39 PM

John, it's because the computer doesn't know it's the gas cap. The computer only knows it's a problem with the evaporative emissions control system, of which the gas cap is one component.

People on these message boards seem so used to dealing with software that they forget a computer is hardware. The computer has to make do with limited information from a finite number of sensors. Adding more sensors, to get more specific information, is expensive; the sensors have to endure heat, road salt, and vibration for a long time, so they need to be durable. Worse, every sensor you add is another sensor that can fail, so you still end up with the "car that cried wolf." Suppose you add a switch to specifically determine that the gas cap is loose. It lights up a "gas cap" light. Is the gas cap really loose, or has the switch gone bad? And if the cap tightens properly, but the seal is bad, you've still got a gas cap problem, but a mechanical switch won't tell you.

The mechanical design of an automobile is very complicated. Pretty much any design decision will involve tradeoffs. People here come across a problem, and say "You should do X to solve it!" but don't think about other problems X will cause, or the aggregate cost of all these solutions. Modern cars can run a very long time, very reliably. The engineers designing them are not idiots--they've thought about these issues more deeply than any of us have. Why be so quick to assume they're morons?

Posted by: mph at May 13, 2005 04:38 PM

There is i simple and cheap fix that the manufacturer can do. Put a black and white LCD screen on the dash panel and if the computer detects an error it will tell you the problem on the screen.

Posted by: unknown at May 13, 2005 05:24 PM

My Passat first did this due to an un-tight gas cap. My mechanic (NOT the dealer) told me that if it happened again, even if it wasn't due to the gas cap, to ignore the Check Engine light unless some other light was on too, and that eventually the light would go out after enough time (or miles or starts, who knows) had passed. I have followed his advice since then and it has worked out fine. The only thing that drives me nuts is waiting for the light to go out. It always does, but sometimes it takes days, sometimes weeks.

Posted by: Alex B at May 13, 2005 06:27 PM

unknown, the display is called a "code reader." It's not on the dashboard, or included with the car, but you can get one for $40 at Harbor Freight. The problem is that the codes do not map precisely to problems; there isn't going to be a code for "gas cap loose" but rather for a problem with the evaporative emissions control system. For a given code, it may or may not be easy to figure out what's causing the code. A cheap code reader can certainly give the advice to check the gas cap for that code, but for other problems you may need the car's service manual, which unfortunately tends to be costly. (Mine was well under $100, and has easily saved me that much, but some manufacturers charge much more.)

I'm actually better off than people with newer cars, because mine is OBD-I, not OBD-II. I don't need a code reader to read my codes--I can just jumper a connector under the dash (with a paperclip) and the check engine light will flash the code. OBD-II brought standardization (so the same reader will read the federally mandated codes from all makes) but I like my old way better.

(I should also point out that my car has 176,000 miles on it and the check engine light has never come on, except in the middle of maintenance when I expected it too. Sorry that many of you seem less fortunate in this regard.)

Posted by: mph at May 13, 2005 07:46 PM

Dave, I'm guessing you must be getting laid a lot, given your obvious respect for women (oh, I'm sorry, I mean 'chicks'). Grow up.

Posted by: ambrocked at May 13, 2005 08:44 PM

Dave, I'm guessing you must be getting laid a lot, given your obvious respect for women (oh, I'm sorry, I mean 'chicks'). Grow up.

Posted by: ambrocked at May 13, 2005 08:45 PM

Everyone else, sorry for the double-post. I got an error message saying I needed to wait a moment and try again. Guess this site's broken too!

Posted by: ambrocked at May 13, 2005 08:48 PM

Dave, I'm guessing you must be getting laid a lot, given your obvious respect for women (oh, I'm sorry, I mean 'chicks'). Grow up.

Posted by: ambrocked at May 13, 2005 08:48 PM

For those of you without a Prius, note that it has a decently high-res LCD screen in the dash. It would be relatively easy for Toyota to place error messages there, along with explanations and suggested corrective action.

Posted by: paul at May 13, 2005 09:51 PM

My check engine lamp lighted and the book said either the gas cap was loose or missing or the catalytic converter was going bad. Was told that the car would have to be started at least 15 times before it would reset. It didn't. Dealer found the two hoses from the tank were split. After some bucks spent it now works fine. Dodge Grand Caravan 2002.

Posted by: jim at May 13, 2005 10:07 PM

MPH. I said it would be a simple fix to integrate the reader into the car. when the CEL comes on it can mean a million different things. If you had a screen it would recieve the code from the computer and then translate it to english and on the litlle screen in the dashboard or high res lcd screen it would say evaporative emission control system problem or error. Also MPH you bought your car before 1996?

Posted by: unknown at May 14, 2005 07:00 AM

Here is a better idea . put a sealed switch where the gas cap goes so when the gas cap in in it will press the switch. if it is loose the switch won't be pressing on the switch. than on your dash it would have a gas cap loose light that would turn on. the switch would be sealed to pervent gas vapor from entering the switch so when you screw in your gas cap you win't see your getting blasted bak 100 feet and you car in flames

Posted by: unknown at May 14, 2005 07:05 AM

unknown, it's quite conceivable that someone's car was built before 1996. Many people can't imagine it, but many people are wasteful (or buy crappy cars that don't last more than 80K miles), too. Mph said that their car has 176K miles on it. It's not hard to believe it's been running since before 1996.

Posted by: anitsirK at May 14, 2005 10:05 AM

i had a 95 pathfinder that had over 200k miles on it

Posted by: unknown at May 14, 2005 11:55 AM

unknown, yes my car is a 1994 model (although I bought it used in 1999). I bought it with about 88,000 miles, and it's up to 176,000 now. In that time, it's needed to be towed once (sudden clutch failure) and needed "field repairs" (a la duct tape) once. I don't treat cars as a disposable item. (But, to be fair, I live where rust isn't a problem.)

I understood your point about showing the code on the LCD, and I essentially agree that it should be easier to get the code--I said how I like my car better than OBD-II cars in this regard. My main point was that the code itself doesn't reliably tell you what's wrong, and most people won't be able to make good use of the information. The people who can diagnose the cause of the code are not, in general, going to be the people who bitch about having to buy (or borrow or rent) a $40 code reader.

Regarding the mechanical switch on the gas cap, I addressed this idea much earlier in the thread. Adding a sensor means both increased cost, and another point of failure. Sensor failures are already pretty common, and the more of them you have, the more the car raises false alarms. I'm not saying that the gas cap switch, in particular, is a horrible idea, but you have to draw the line somewhere--adding a cornucopia of sensors to precisely pin down every problem leads to excessive cost and complexity.

Posted by: mph at May 14, 2005 12:19 PM

BTW, unknown, in my last post I didn't mean to suggest that *you* treat cars as a disposable item (I see you've kept one to old age), but there are a lot of people who do.

Posted by: mph at May 14, 2005 12:20 PM

I'm going to have to agree with mph's analysis here for a variety of different reasons, but they all boil down to one thing: he's right.

For 17 years I drove third-hand vehicles I maintained myself: A 1983 Toyota Cressida that caught fire (over 100,000 miles, but can't remember just how far over), a 1985 Honda Accord that hit 174,000 miles before all the seals sprung more leaks than the Clinton White House, and a 1988 Toyota Camry that went 133,000 miles before the clutch disintegrated. I changed my own oil and filters religiously (probably why they lasted so long), and such things as headlights, seals, plugs, wires and belts as necessary.

When the last one finally died, I bought my first brand spankin' new car. I love driving it, but the experience still sucks. Why?

* The damn check engine light comes on for exactly the reason discussed in this thread, and won't go off until the DEALERSHIP resets it.

* The oil filter is located in the back bottom of the engine behind a skid plate, and the car has to be jacked up and partially disassembled to do a simple friggin' oil change--at the DEALERSHIP, because nobody else stocks the oddball size filter it takes.

* The headlights are $40 instead of the $10 at Wal-Mart I was used to, and have to be installed at the DEALERSHIP because the front end of the car has to be disassembled to access the headlight module.

* I'd get a repair manual and try this myself, except the car is held together with a variety of clips and plastic doodads that break upon removal and must be replaced, and you can only get them at the DEALERSHIP.

Basically, the car has been very carefully engineered to make sure it goes back to the DEALERSHIP for everything to keep your $$$ rolling in to THEM, and make sure it doesn't (because it CAN'T) go anywhere else.

Before anyone asks, I'm not mentioning the make because EVERYBODY makes their cars this way now, and besides this bit of engineered enforced loyalty I really love the car--and my point is that as much as the car rocks, I refuse to recommend any company whose product puts you through this experience. Since they all do it, it's a moot point anyhow. But darn it, the damn check engine light comes on all the freakin' time, and the first car I owned that never happened even when the thing caught on fire. One light for everything doesn't tell me diddley squat, but rather cries wolf until I ignore it completely. At least let ME know what the code is by a dashboard readout, and let ME reset the damn thing if I want to.

I have a friend who rates vehicles according to how much road he can see under the engine when he lifts the hood. More road=better car.

I'm starting to think he's right.

Posted by: Erich at May 15, 2005 04:12 AM

the check engine light doesn't actually mean anything anyway. they just put them in to freak people out.

Posted by: Bob at May 15, 2005 09:49 PM

My Passat did this (boy, I'm glad I'm not the only one that had this problem as I see all the PASSAT entries posted). Here is a secret. Most cars still talk ODBII (Even though the dealer said it was a CAN bus NOT ODBII compatible). Run down to Autozone and have them reset the light.. It's free, and for me at least, it was on the way home.. Better then that nagging light (Which if I remember you can turn off via a setting with the VAG-COM tool) BTW, they will run a code check, not only turn off the light, so you can indeed see if it is a "loose gas cap" or something major. For my wife- it was a hose that melted, and it was a quick 5 dollar fix compared to 200+ the dealer wanted (80 of which was to get the code)

Posted by: Erik at May 16, 2005 08:47 PM

Took about the same ammount of time to fix the same problem on a 2003 Nissan Maxima. Really stupid and annoying problem

Posted by: Seth at May 18, 2005 06:28 PM

the reason you need to drive the car for 20 minutes 2-4 times is so that the pressure in the gas tank can fully build up again.

Posted by: Justin at June 1, 2005 02:50 AM

If a passenger mentions the check engine light in my '89 Tempo I'm going to say, "Oh that light means the car is really really old."

Posted by: Timm at January 24, 2006 01:41 AM

Here's a trick anyone can use to turn off the check engine light. But I wouldn't recommend doing it if you don't know what's wrong with your car in the first place. All you need to do is unplug both - & + battery terminals or you could leave your lights on until your battery completely drains (that's how I found out it could be done)Why both terminals and not just the negative? beats me. I just now it won't work if you don't unplug both. I Guess you could always do this the first time your light comes on and if it turns back on again later on, then you know their might actaully be something wrong with your car and bring it to a repair shop.

Posted by: fred at May 27, 2006 04:25 PM

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