Check Engine light

bblaha · January 2001

I could be wrong in this, but I'm pretty sure the CEL (and the whole electronics/sensors/computer system) is a direct result of a push for lower emissions and/or better fuel economy. You need a bunch of sensors to keep everything running optimally in order to keep the emissions down/mileage up; when a sensor decides something is a little out of whack, it turns on the light forcing you to make repairs to get it back ... ummm ... in whack.

0patience · January 2001

The check engine light and all the sesnors are indeed a direct result of lowering emissions and fuel economy, but also a result of electronic fuel injection which is more efficient and more power and lower emissions as a result.
The first of these vehicles started around 1982 and were few, then they gradually became more and more.
Now,understand that the CEL is a tool to use to keep your vehicle from tearing itself apart.
While pulling the bulb or taping over it makes you not see the problem, it is still there.
I've told this story before, but here goes again.

This guy cames to me,cause his engine won't run, I take a look, he has tape over the check engine light. I asked him about it and he said it and he said it came on about a year ago and some moron had told him that it was nothing and to tape over it.TO make a long story short, the codes pulled were everything,but the oldest ones had to do with the spark timing and O2 sensor circuits, had they been repaired, the cost would have been a few hundred dollars.
But since he decided to tape over it and run,the repair cost was a new engine and catalytic converter,about $4,000.
See, the spark timing had advanced the timing and created a problem with fule mixture as well as eventually burning a hole in a piston,that took out the O2 sensor which eventually clogged the catalytic converter until the vehicle wouldn't run anymore. That's when it came to me.
Then he had to make the decision to junk the vehicle or replace the engine,O2 sensor, EGR valve and catalytic converter.
So that little piece of tape let him run for about 9 months,but cost him,bigtime.
So,if you want to ignore the check engine light, more power to you, but if you live near me, you will be seeing me, one way or another. LOL!

7937 · January 2001

I used to have a 1986 Honda Prelude. There were 2 things that intermittently brought the check engine light on. By the way, the computer code was easy to get to because if you removed the rear left hand ashtray you could see the LED blinking out its code.

A lazy oxygen sensor was one thing that brought the check engine on on occasion and the other was the EGR valve. I changed the oxygen sensor. The EGR valve was difficult to get to but I found that by removing the vacuum pipe and putting a pipe on the onto the EGR valve and sucking it a number of times, the car would go for months without the check engine light coming on again. Seems like the EGR valve was sticking at times and moving the diaphragm up and down freed it up.

bernald · January 2001

Thanks for the input. I guess the only thing to do is to go to another dealer or another repair shop. I'm also thinking of having the car checked out by AAA. Finally, I could always sell it - with full disclosure, of course.

toddmodem · February 2001

Hi everyone,

I have a problem that some of you experts out there can possibly help me with. I recently added a bottle of Wynn's Exhaust control to my car and lo and behold, the "service engine soon" light came on. I definitely believe that this is directly related to the additive since the light has only come on when I changed brands of gas (ie: Esso to Petro Canada) I'm wondering how I can clear this code as I'm about to trade the car in and it looks pretty bad when the SES light is staring the dealer right in the face!! How much is a code scanner (I think I've seen them at Canadian Tire)? Will disconnecting the battery do it? Is there a fuse that I can remove on the 96 Saturn SL1? Thanks for your help

Cheers
Todd

alcan · February 2001

Remving the battery cable or a fuse will not erase trouble codes on a 1996 or newer car. You'll have to use a scan tool. Almost any shop will have one.

toddmodem · February 2001

Thanks, I had a feeling it wouldn't work. Out of curiosity, do you have any idea how long the OBD computer can retain the information? I assume that it's like a motherboard and must have some sort of secondary power source. A CMOS battery or something.
BTW -I found an OBD II scanner at Canadian Tire for C$249.00. I'm sure the problem will go away after a tank of gas, so I don't think it's worth the expense (OTOH It might be useful in the future. Do 2001 models use OBD II or are we at OBD III?.
Thanks again!!

Todd

7937 · February 2001

Codes on OBD2 systems stored in the computer should last forever untill erased by a scanner. Even when the battery is disconnected. A non-volatile memory system is used. That means when the CMOS logic system is switched to a zero or one it will stay that way when power is disconnected. Only a scanner will erase it on OBD2 systems. A perfectly good scanner can be had for under $200. I use the Actron CP9035 and I once saw them on special for $164. It's worth its weight in gold.

7937 · February 2001

toddmodem, If I may hazard a guess as to why your check engine light came on after adding Wynns Exhaust control, I would say that yor oxygen sensor has gone on the blink. I'd be very leery of putting any additives into the fuel.

toddmodem · February 2001

Thanks for the advice everyone. I certainly won't be adding anymore additives to the fuel!! I went out this morning and tried the old battery disconnect trick for 15 minutes and it worked!! Maybe it's just a coincidence as I understand from the previous post that it should have no effect...oh well!

Todd

autojoe2 · February 2001

I know alot of codes will clear themselves if they do not detect a fault in a certain amount of time.Take for instance on FORD EEC-V,OBD II,oxygen sensor circuit,if a problem with the heated oxygen sensors is detected on two consecutive drive cycles,the MIL will illuminate and a DTC will be recorded.The MIL will go out after three consecutive trips without a repeat failure.After the MIL is extinguished for the stored DTC,the code will be automatically removed after 40 consecutive warm up cycles without the fault reappearing.I notice this with EGR monitoring and misfire monitoring ect.So the PCM has the capibility of removing stored DTC'S if not detected for the programmed time limit.This relates only to OBD II.

7937 · February 2001

There certainly are codes that will go off if the fault does not persist. It all depends on the programming of the computer. However, if an OBD2 computer is disconnected with stored codes it should retain those codes. Just be sure that the check engine light that went off after disconnecting the battery doesn't come on again. There's always the possibility that some fault is still lurking around there. Many faults only come on after so many cycles. As I said, it all depends on how the manufacturer programs the computer.

7937 · February 2001

Come to think of it, a good example of what I am trying to say is that if you take a car with an electronic odometer as on some GM models and disconnect the battery, when the battery is connected again, the same mileage as before will be shown. It does not reset to zero. In fact, the digital readout on the odometer is coming from the computer. Even if you leave the battery disconnected for a week, on re-connection the same miles will be shown. So there's no chance of turning your miles back to zero... he he he.

karl6229 · February 2001

The Service Engine Soon light appeared. I took it to my dealer. I got the runaround, $100 for them to diagnose. I took the keys back and left. I checked the gas cap and made sure it clicked 5 times. I have noticed no difference in performance.
After checking the net for info, I found this board. Does anyone know where I can find the actual contents of TSBs. I have checked nthsa, and alldata, but these sites only have title and summary info. Any suggestions?

alcan · February 2001

All late '95 and newer cars and light trucks are equipped with OBD-II on-board diagnostics. The only way to extract diagnostic trouble codes is with a scan tool. What do you intend to accomplish re TSB's?

xwray · February 2001

You may need to leave it disconnected an hour or two depending upon how much residual charge is retained by your ECU.

7937 · February 2001

xwray, will it also clear the miles on an electronic odometer? My 99 Chevy has an electronic odometer and I've put the car battery into another car to get me going and days later, after installing the battery back into the Chevy, the odometer shows the same mileage again. I mean let's face it, this offers the possibility of turning back electronic odometers if the memory is lost when disconnected from a power source. Modern car computers have memories that are very much like solid state audio recorders. You can record music on these chips and leave the batteries out and months later you can still play that music back when you install the batteries again.

Anyway, I think it's an interesting subject and worthy of discussion. I think automobile computers are keeping pace with computer development in general and we must not underestimate them. I've even read that some car manufacturers are installing unbeknown to the owners, "black boxes" into cars to plot the drivers actions, speed of vehicle, and so forth just before an accident. Big brother is watching you!

7937 · February 2001

I quote from the manual of my digital answering machine - "messages are stored indefinitely on a "flash memory" IC chip and will not be affected by power failures. All of the messages are saved until you erase them. Unquote.

They could just as well have been describing the operation of the memory of a modern automobile computer.

xwray · February 2001

There are two basic types of memory being used here - volatile and non-volatile. The odometer uses non-volatile memory which is similar to the flash memory used in cameras or the BIOS of your PC. This type of memory is not reset or cleared when power is removed and takes a deliberate action to clear...easy enough on the camera memory but not so easy on the odometer because it is generally not physically accessable and probably does not have the logic terminals available to be electrically erased to prevent tampering...depends on mfg design. Volatile memory is like the RAM in your computer...turn it off and it loses everything; ir, it is erased. The trouble codes stored in the engine control computer generally use RAM to store these codes (I know for a fact my Lincoln LS does) which, like your computer, when turned off will lose the data stored in memory - any learned drivability parameters as well as trouble codes will be lost
(that's why your car may run rough for a few miles after disconnecting the battery...it needs time to re-learn the drivability parameters). Note that a mfg can design any kind of system he desires so it's possible that not all vehicles adhere to this design...try it and see but wait long enough for any voltage stored in the computers internal capacitors to bleed off so that power is indeed removed from the memory.

0patience · February 2001

I've had vehicles with the batteries disconnected for days and the codes that were there before were still there whan the new engine was fired up. The codes had to be cleared by a scanner to confirm that no problems were present.And if your theory were correct, then disconnecting the battery for more than 30 seconds would clear the codes, which it doesn't.

xwray · February 2001

My Lincoln LS coughed up a P0455 code. As you know this is the sometimes hard to find LARGE EVAP LEAK code. I'm trying to run it down myself since there are no drivability issues and I don't want to use a dealer unless there is no other way. Before I bought my scantool, I disconnected the battery to clear the code. I have also read in other places where this worked for a given model. Obviously I haven't personally checked each and every variation out there (I think I indicated that the way this was implemented was determined by the mfg design). Do you know if the ODB II spec maddates that trouble codes be stored in non-volatile memory. If that's not the case that might explain why some vehicles codes can be cleared by a battery disconnect and others can't.

br2k2 · February 2001

I first noticed my EL within 20 days of buying my 1992 Ford E-150 conversion. Codes showed up, but replacement of those items didn't help, and the same codes kept reappearring, or no codes showed up. I finally figured out it was the fuel pump - replaced it 2 weeks ago, and haven't seen the EL since. Try it! Also, check prices on the pump - I was charged $286 for the part, only to find it at Discount Auto for $129.00 minutes later - same exact part, same packaging, etc.

adc100 · February 2001

had the dreaded "service engine soon" light lit after 25 miles. Dealer said the problem was solenoids in the auto trans. When they removed the auto trans/torque converter there was abnormal wear on the torque converter. Nissan couldn't figure it out, but they are giving me a new auto trans/torque converter. I guess it pays to take the light seriously some times.

Al

eddiemad · February 2001

Hi.. my wife has a '99 Montana with 42,000 mi on it. The "Check Engine Light" just came on. Was wondering if this light is programmed to come on at this time for periodic maintenance (oxygen sensor, EGR, etc) or if there's actually something wrong with the engine. Has anyone else had this light come on in a GM minivan and, if so, what was the problem? Thanks. BTW.. where's the reset switch?

alcan · February 2001

The CEL comes on because the powertrain control module has seen an input from a monitored sensor or circuit that's out of specified parameters. All late '95 and newer vehicles are equipped with the OBD-II self diagnostics, and the only way of extracting stored trouble codes and turning off the CEL is with a scan tool. There is no "reset switch".

waynerp · February 2001

The check engine light on my wife's 2000 Beetle 1.8t has come on at 35K miles. No other symptoms of a problem - runs fine. This ocurred a few days after I changed the oil, oil filter, and air filter. I've checked the gas cap, re-checked the air box and elsewhere under the hood and found no obvious problems. The dealer says this is probably not covered by the warranty - they won't know until the code is checked. Anyone have a similar experience with a VW or Audi 1.8t? Thanks for any advice.

theiceman · February 2001

I was loosing vacuum in several functions on my 1995 Villager and the CEL would come on intermittendtly. Finally diagnosed it as a small ECR hose ($15) and the light illuminates no longer.

kvd1 · March 2001

I hope somebody might have a clue what's wrong with my car. I have 96 Chevy S10 4.3L, 90K Miles, and the SES-light comes on. I've reset it a few times and read the codes. Sometimes only 0101 comes on, which indicates a MAF sensor range/performance problem. Most of the times it comes with code 0420, which indicates a Catalyst System Efficiency below Treshold, or it comes on with code 1406, which indicates an EGR Pintle Position Circuit Fault. Never all 3 codes are stored. The engine has a lack of power and sometimes it shakes, with the gas pedal half way down. The light doesn't come on until the engine is at operating temperature, like after driving for 6-15 miles or so. Has anybody had this problem before? Or can anybody give me an indication what it possibly could be? Thanks!

erikheiker · March 2001

1991 Dakota, 318, Check Engine Light has been on for last 10k miles. Totals miles are 135k. Is there an easy way to reset the light? What are the most common reasons at this age for the light to come on? Truck recently failed emissions test solely because the light wouldn't go out. They look for it to light up at engine start so unplugging, although the obvious solution, isn't an option. Thanks for any input.

Erik

alcan · March 2001

Turn the ignition key on-off-on-off-on within 5 seconds (don't start it). Count the flashes on the CEL. Eg blink.....blink, blink = code 12. Disconnect battery for 30 seconds to erase stored codes. Post your findings or go here and click Technical-Trouble Codes:

http://www.batauto.com/Chrysler.html

kvd1 · March 2001

Does anybody have an answer to my question, posted in message #429 ???

alcan · March 2001

Try here:

http://www.batauto.com

kvd1 · March 2001

Thanks, I also posted the same question there.

erikheiker · March 2001

Thanks for the info. I went to the link you provided, but it only gave the sequence for a code 12. How do I decipher other codes? Thanks again.

Erik

alcan · March 2001

Erik, I'm not sure I'm reading your post right. Were you able to access a code 12? That indicates the ecm was put into diagnostic mode and any stored fault codes would have been displayed as additional sequences of cel flashes. If code 12 only was displayed there were no stored fault codes.

btenvy · March 2001

I have the check engine light constantly on for about a week now. The car runs great once it starts no hesitation or like problems. However the problems occur when you run the car turn it off then try to start it less than an hour later. Symptoms are: the car will start but then die. If you leave the car and come back later it starts just fine but he check engine light is still on. Any ideas? Any help would be useful. BTW- the car has 30050 miles.

Thanks,

Jarvus

alcan · March 2001

Your car is OBD-II compliant and requires a scan tool to retrieve the stored diagnostic trouble code(s) causing the MIL to illuminate, and to erase the codes after the condition has been corrected.

erikheiker · March 2001

The truck belongs to a friend so we haven't checked out the codes yet. My question was about codes other than 12. Now I know how to decipher them too. We'll check it out this weekend. Thanks for all the info and the link.

Erik

btenvy · March 2001

About how much for one of these scanners and where are they available? Also, is there a place to find out what each code means? Any other help is also appreciated.

Thanks,

jarvus

bblaha · March 2001

If you scan way back, 0patience posted links to 3 different kinds. The cheapest is about $200.

btenvy · March 2001

About how much for one of these scanners and where are they available? Also, is there a place to find out what each code means? Any other help is also appreciated.

Thanks,

jarvus

btenvy · March 2001

thanks

btenvy · March 2001

could the aforementioned problem be as simple as a plugged fuel filter?

alcan · March 2001

Possibly, if it was causing low fuel pressure and a lean fuel mixture. Could also be something as simple as a loose gas cap too. You'll find a list of generic OBD-II codes here:

http://www.batauto.com/obd2.html

It's probably a powertrain code so click on OBD2 "P".

btenvy · March 2001

alcan · March 2001

Don't forget that if you do pull stored trouble codes the job's only 1/2 done. Often there's a problem causing a sensor to supply an input which is out of specified parameters, which will cause the CEL to turn on rather than the sensor itself being defective. Don't shoot the messenger. Eg: a defective fuel pump results in low fuel pressure which causes a lean condition driveability problem and a CEL. The scanner reports "O2 sensor lean". The $80 sensor gets changed. Any improvement? Nope. The pump's still defective. A scanner will take you to the right street but it usually doesn't know the house number.

0patience · March 2001

Currently there are several scanners available for the OBD2 system that are PC based or hand held that are around $200-$300.

A bunch of us are reviewing a bunch of these scanners to see which,if any would be able to provide easy use and good info for folks.

I, along with a bunch of other mechanics have a list of links for the scanners at this page under Scanners and Diagnostic Tools heading.

Hope this helps.

0patience · March 2001

A scanner will take you to the right street but it usually doesn't know the house number.

I love it! That is a great way to describe it.

97jettagtgrl · March 2001

The check engine light came on to haunt me with 18000 miles on the car. I was in an accident the week before, someone hit me on the side panel, very minor, it was in a parking lot. I drove it days afterwards, then the engine light came on. My friendly neighborhood mechanic took a look at if for me and saw no problems, like a hose loose. He told me it was VW's problem, and if they dont want to cover it under warranty to fight it. I am going to VW tomorrow for my service, and after being there to make the appointment i found them quite rude. I am a 19 year old female who purchased the car herself and will not be pushed around!! anybody with advice on how to handle the mechanics??

Mr_Shiftright · March 2001

Well, you have to look over your warranty yourself, and if they deny the claim they should explain to you why this is so...ask them to point to the exact page and sentence that shows that the part that is defective is not covered, and why this is so. If they do point it out and it seems like they are right, then you lose. I suspect you may be out of warranty on time, although not on mileage, but also it may depend on the part affected. I don't have a copy of the 1997 warranty handy...perhaps you can tell us what it says in terms of time and mileage. It should all be in the owner's manual.

Check Engine light

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