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Check Engine light

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  • bnormannbnormann Posts: 335
    ...doesn't go out right away. The computer looks at a running average. It will take some period of time before the "paranoid" computer thinks that "Everything's OK".

    Bruce
  • I need to find out how to read the fault codes on a 91 Olds 88 W/3.8L V/6. The car only has 6500 original miles on it and the Service Engine Soon light just came on. The engine idles and runs fine. It belongs to a widow and is seldom driven although started up on a regular basis. I have digital and analog voltmeters. Will I need some sort of code reader to determine the codes? She was told that it was likely a sensor, but I would like to be able to determine which one.
  • lotusmanlotusman Posts: 6
    For many years, or so I am told, GM relied on Lotus engineers to do the designing for their engine controls. My 1989 Lotus uses the MPFI system which they designed for the Corvette. I is the system used for their fuel injected cars. I found the codes for my system were like those for the 1988 Tempest in the Library. I corroborated these with the shop manual for my system.

    Regarding clearing the codes: Take the battery cables off. after several minutes they will clear. Return cables to their posts. As for how to get codes on a GM vehicle, at least with the MPFI system, where ever you find the plug on which they plug in the scanner at the shop, (This is not always easy to find.) there will be an "A" and a "B" pin location designated. Turn the ignition on but don't start the engine. I use a paper clip to short the two terminals. The check engine light will start to blink once, then twice or a 1-2 code three times. After that the codes will flash with blinks for three times then go on to any other trouble code there may be and repeat it three times. When no codes are left, the light will flash the 1-2 code three more times. As I said, check the Library for the car manual and the codes.

    My Lotus has had a "26" code for the three years which I have owned it. This is for "Quad Driver Module" which is longhand for it checking sensors and wiring. Or basically everything if you see the two pages of possibilities in the manual. I finally went to the dealership to see what their "Tech one" scanner showed. It said it could be three different things but the bottom line was that if no other symptoms are evident, "DON'T WORRY". My car still gets 25 MPG and will easily do 130 MPH.

    I do appreciate the possibilities ya'll have stated and I will try them out.
  • 0patience0patience Posts: 1,542
    Here are webpages for retrieving codes on pre 96 vehicles,click the manufacturer you need to retrive the codes on and it will take you there and there is also a codes list too.Some 95 and all 96 and later vehicles have the later OBD2 system and can only be retrieve with a scanner.
    GM code retrieval
    Chrysler code retrieval
    Ford code retrieval
  • 0patience0patience Posts: 1,542
    It will probably make it easier if you print out the page you need.That way you can bring it to the vehicle with you.
  • Just wanted to thank Lotusman and Opatience for your assistance. This is exactly what I was looking for. You made it a simple job to get the computer codes.
  • phylpphylp Posts: 49
    It appears that a hole in the vacuum line was causing activation of the "Check Engine" light on our Passat. Thanks for all the good help on this "mystery."
  • protravelprotravel Posts: 19
    The check engine light is just a manufacturers, legal scam. They write tight factory codes in the system chips, and ANY variance will throw a check engine code.

    This is now my fourth year, and 60,000 miles, with a brightly burning check engine light, Should burn out soon!

    Think about it. $65.00 and hour times one million check engine lights, you do the math.
  • 0patience0patience Posts: 1,542
    I suppose the oil light,alt light and temp light were all scams too.The specs for the computers on vehicles are actually quite broad and in or for a check engine light to come on and stay on certain things have to happen.A hard fault code must be set or multiple temperary fault codes must be set in a given amount of time.Or the same fault code must have multiple settings.But itf a temporary fault code sets the light and it isn't a continuous code,then it will clear itself and turn the light off.If the light has come on and is staying on,then a hard code has set and there is a sensor problem.As I said before,if you want to ignore the light,hey,more power to you,but some people take pride in their vehicles and if you know what is causing the light,no big deal.If the vehicle is 95 or earlier,there are ways to retrieve the codes yourself and I have given links for the domestics,and if anyone needs other vehicles I have those too.After 95,the federal govt. regulated that the systems in vehicles go to a system by all of them,the OBD2 system and it is only retrievable thru a scanner.Scanners run from $399 and up.Really,please do your homework before making some statements as some people actually believe what is written.
    I guess most of you knew I wouldn't leave this one alone.Ha ha.
  • I have a 96 Ranger p/u. My question is: Can a mechanic intentionally cause the engine light to come on - could he pop the hood and pull some wire or something. My story: I pulled into a Firestone shop to pick up some new wipers. I was going to put them on myself but it was almost free for them to do it. After 15 minutes, the truck comes out and the tech gives the key over to the desk and tells him something inaudible to me. The desk guy is says " oh (my name) your check engine light is on" using a tone of seriousness in his voice. I quickly sensed that he was hoping that I would panic and beg him to turn it off. I didn't fall for that. My light just happened to come on now! BS. I know they did something, for I was at this shop before and I haggled with them on the price of a new tire / wheel alignment. I also needed brakes at the time, and I told them somebody else would do it. I guess they don't particularly like me. Of course I just may be paranoid and it's just a coincidence that my light came on during a wiper change???
  • 79377937 Posts: 390
    To remove any doubt as to why the check engine light comes on, just invest in a $200 OBD2 diagnostic tester. The scanner will tell you why the light came on and codes can be erased once repairs are made. Even if you cannot repair the car yourself you will at least have an idea of what to expect from your mechanic. Actron makes a scanner that covers all OBD2 (from 1996 upwards all have to be) imports and local cars for $200. Visit their site at http://www.actron.com The model # of the scanner is - CP9035. I don't regret buying myself one.
  • 79377937 Posts: 390
    Look out for this one! On OBD2 the computer also checks for fuel tank pressure and if the engine is running while the gas cap is off or loosely fitted, the check engine light will come on. After a few stop and run cycles with the gas cap properly fitted it should go off. Meantime, before it goes off you could be sweating wondering what has brought the check engine light on. Also a source of income for dishonest mechanics however.
  • butch11butch11 Posts: 153
    It is really easy to make it come on-pull off a plug wire with the engine running-on it goes. If you have the time and there is a crusading tv station in your area-call the news desk-ask them if they would like to help catch a crook.

    Would suggest you never go back to that den of thieves.
  • skyrmskyrm Posts: 10
    I have a 1996 Geo Prizm with 84000 miles. My wife put on 80000 of those, and a few weeks after I started driving it, the check engine light came on. Took it to a local service station, they kept it 2 days, couldn't find anything wrong, and turned the light off.

    Now, 3 months later, it came on again. Decided to take it to a local Chevy dealer. The ran the diagnostics, and told me I need a new 02 sensor and a new ECM. $1400. Ouch.

    Having a basic distrust of dealerships, I decided to try and get a copy of the diagnostic report, to get the numbers that came up. It took 2 days, and they said they don't print them out, the tech just writes them down. Hmmmm..... Dealer just moved into a new humongous building, all new stuff, and they can't get a printer for this stuff?

    Anyway, they say the number was PO136. I checked the GM codes that were posted in this forum, and they were all 2 digits #'s. I'm I being taken for a ride? Anyone able to help, I would greatly appreciate it!!!

    Thanks,

    Steve
  • locke2clocke2c Posts: 5,038
    Oops, almost forgot. Under OBDII there must be at least two o2 sensors. One before any catalysts and one after at least one catalyst. Even replacing both won't be that expensive.

    -Colin
  • locke2clocke2c Posts: 5,038
    That's an OBDII type code Steve. P=Powertrain. To know the rest I'd have to not be sitting here at work. ;)

    Buy an o2 sensor yourself, they are not expensive. Replace that and then disconnect the battery overnight. Reconnect in the morning and when you start the engine, let it warm up and don't touch any controls until the idle stabilizes. This should reset any soft codes.

    After that if the light comes back on then you can consider additional repairs. I wouldn't want to just fork over $1400 without trying this first, and I'm sure you feel the same.

    -Colin
  • skyrmskyrm Posts: 10
    My wife and I thank you for the quick response! We have a guy who can install the sensors, I have no idea where they even go. We'll see what happens, and let you know.

    The guy at Chevy told me that probably what happened is the O2 sensor overheated, and shorted out the ECM. Wouldn't the car stall or run rough if the ECM was bad? I thought that thing was relatively important? The car runs fine.

    Thanks again,

    Steve
  • 0patience0patience Posts: 1,542
    It is the one farthest back and not necessarily the sensor itself.Forget the ECM as the problem,it is not.If the ECM was the problem,then it would either throw more codes or make the engine run rough.Have an independant shop check the O2 sensor circuit only.
  • skyrmskyrm Posts: 10
    We have a guy who will look at that for us. I guess the dealership just figures that we will believe whatever they tell us. NOT!

    Thanks again - you've been a big help to us and many others here.

    Later,

    Steve
  • 0patience0patience Posts: 1,542
    I have a webpage with the generic OBD2 codes and their definitions(some OBD2 codes are manufacture specific and are not listed).Click on the link and it will take you there.
  • 79377937 Posts: 390
    Steve,
    From my knowledge of electronics I can tell you this. I have not had hands on experience of automotive computers but the same would apply in your case. The oxygen sensor is a low voltage high impedance device and its typical operating voltage ranges from 0.10 volt to 0.90 volts output. The input resistance to the computer from the O2 sensor is high. Therefore, the computer should suffer no damage should the O2 sensor go short circuit.

    Only in the case of a low impedance output from the computer as in the driver for an injector for example, is it possible that damage may occur if that output is shorted. Hopefully, the computer fuse would have blown first.

    To sum up. I think that the mechanic that told you a shorted O2 sensor damaged your computer is taking a chance.
  • 79377937 Posts: 390
    I have read through these postings again. I cannot understand why a mechanic would knowingly let a person drive a vehicle with a bad O2 sensor as in the case of Intique41.

    The O2 sensor is one of the most important devices in in the system and is cheap and easy to replace. It allows the computer to go into "closed loop control" in order to fine tune fuel consumption and emissions. If the sensor is bad the computer runs in "open loop mode" and, eventually, "limp home" mode with a loss of performance. If the fuel mixture is too rich there is also a danger of damaging the catalytic converter. How on earth does such a vehicle pass a smog check anyway?
  • skyrmskyrm Posts: 10
    We will have the O2 sensor replaced asap. I'm sure it won't cost $1400. My wife and I really appreciate the help.

    The dealer that we went to is advertising that they are adding a hair salon and diner to their building. I guess they plan on customers spending ALL their money there.

    Later,

    Steve
  • skyrmskyrm Posts: 10
    Took the Prizm to the guy my wife used to take the car too when she was driving it, and he said it is only the O2 sensor. Will be $320 or so. Man, is that an expensive part.

    Oh well, beats $1400!!!

    Thanks again,

    Steve
  • wenyuewenyue Posts: 558
    $320 isn't so expensive when comes to that kind of replacement. Keep in mind that your Prizm is just a rebadged Toyota Corolla. And import car's parts and labor tend to cost more than domestic cars. But, with Toyota's reliability, you should only very sedomly need repairs.
  • skyrmskyrm Posts: 10
    This is the first major work we've needed, and the car had 84,000 miles after only 4 years. Not bad. It's a nice little car, and I can fit my drums in it, so I'm happy.
  • 79377937 Posts: 390
    When I took my 86 Honda Prelude for a smog check it failed because the O2 sensor was bad. Total cost for parts and labor to replace by service station mechanic while I waited - $170. If you can replace it yourself it will be cheaper. You can use a generic brand. Bosch makes them for all makes and model cars. In fact as far as I know, most automakers use Bosch. Just get the right one suitable for your car. I have some idea in my mind that they cost around $80 or so.

    The O2 sensor in the Prelude was marginal and did not bring the Check Engine light on. However, after replacing it the car passed the smog check with flying colors. I also noticed a distinct improvement in performance.
  • 0patience0patience Posts: 1,542
    You are a little off on your price quote,if you can find an O2 sensor for a 96 Prizm for $80,let me know where you can buy them.My cost at Jobber prices(wholesale)for Bosch O2 sensor for the Geo Prizm is around $100.ExpressAuto Parts has BorgWarner O2 sensors for around $100,if it is a Calif.model then the sensor is around $150.ExpressAuto Parts is about the least expensive on the internet.
  • 79377937 Posts: 390
    Opatience, as I said, it was a price I had in my mind. I did not state it as fact. The O2 sensor was replaced in the Honda Prelude more than 3 years ago and that might have been the prevailing price then. I have lost the detailed statement but I know that the total bill for parts and labor was $170 3 years ago. However you look at it, $320 is pretty steep for the Geo Prizm.
  • 79377937 Posts: 390
    Opatience, by the way, I forgot to add that the ignition timing also had to be set and this was also included in the total price of $170. I stood by while the mechanic did this so I know that it was done. I also watched him fit the new O2 sensor.
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