Check Engine Soon Light Question

[profdlp]

A while back my Check Engine Soon light came on. Not wanting to be at the mercy of a mechanic and his little diagnostic machine, I did a little research on the subject. According to the info I found, it is preset at the factory to warn you that it's time to replace the PCV Valve when you reach the exact mileage my car was at when the light came on. I dutifully replaced the PCV Valve and didn't give it much more thought. The gas mileage is still great and there have been no other warning signs (like burning oil, hesitation, etc). Since that happened I have passed two emissions tests in Virginia and two more here in Ohio, each time with a reading which barely registered on the scale. I'd have to dig out the paperwork from last year, but as best as I can remember it was way less than 10% of the maximum value which would still allow you to pass the test.

My license plates expire in a week and I need to have the emissions test done in order to renew them. When I had it done last year the guys at the Ohio E-Check station didn't even want to test it. They told me that having the light on at all meant that I automatically failed. I gave them the old "pretty please" routine and asked them to test it anyway, pointing out that I at least wanted to know how serious it was if I had to take it to the shop for repairs. (Back in Virginia the emissions testing is done at the same local gas station where you get the annual car inspection performed and it's not unusual for a dishonest mechanic to try to talk you into expensive work if you happen to flunk, which is nice for them, but not for the <s>poor sap</s> customer who doesn't have access to his own test equipment.) When the car passed with flying colors they gave me the magic papers which let me renew my tags.

Included with this years license plate renewal form there is a little note saying that there will be no exceptions to the Check Engine Soon light being on; you will flunk, period.

The local place where I have had my car serviced for the past two years wants $70 just to hook up the little mini-computer and get the error code. According to them, without the diagnostic device it is impossible to make the light go out. (I guess they have never heard of linesman's pliers.) They also mentioned some ominous-sounding things which could be causing the problem, such as a bad Oxygen Sensor.

I'd like advice regarding these points:

1) Is $70 a fair rate to plug in a probe and read off a number? I know that they have to pay for the machine, but good-gosh-golly.... :eek:

2) What would one expect to pay to replace an Oxygen Sensor on a 1997 Geo Tracker 4WD vehicle? Is that likely to be the cause? Is this something that a person who is handy with tools and has a lot of experience fixing machinery would be able to do themselves - without risking adding a towing charge to the bill?

3) I found info on the Internet which says that there is a hidden slide switch under the dashboard which is used to reset the light after something like a PCV Valve replacement. If the light stays out, you know that you have no other problems. If it comes back on, you know that something else is amiss. The mechanic says that there is no such switch. Even if he's wrong, I can't find the stinking thing to save my <s>wallet</s> life. Anybody know anything about this?

Let me make it clear that I'm not trying to beat the system. If the car needs work and/or is polluting the air I want to get it fixed. I just don't want to pay money I don't have to fix a problem which isn't really there to begin with.

Lastly, this repair shop has been very fair with me in the past. I had a bit of a problem over some major work I had done last month (brakes and A/C), but the owner was quite reasonable in addressing my complaints. Bottom line, I do have some trust in these people or I wouldn't be going there at all.

Any advice would be greatly appreciated. :)

[Mt_Goat]

Depending on make and model there is often a series of things that the average person can do to reset the light. Right the only thing I can think of would be to disconnect the battery and discharge the system like resetting your cmos.

[QCH2002]

If they had only equiped cars with jumpers to allow us to clear the CMOS :D

[profdlp]

...disconnect the battery and discharge the system like resetting your cmos.
I had the battery die on me not long after this happened, but there might have been enough juice left to keep the onboard electronics going. I'm going to try this tomorrow. :cheers:


If they had only equiped cars with jumpers to allow us to clear the CMOS :D
I've got my linesman's pliers ready, just in case... :ninja:

[GHoosdum]

Steve, there are a variety of ways in which you've been misled by these mechanic clowns. Hopefully I can lend a hand. (Larry and Q are actually right on the money)

1. The Check Engine Light goes on, in 90% of cases, due to an emission item. In my wife's car, for instance, the CEL will light if the gas cap is not tightened at least four full clicks. In most cases, you don't need a tow.

2. Seventy bucks is a complete rip-off to read the code. Why? In all 1996 and newer vehicles, there is a connector called an OBDII (On Board Diagnostics 2) connector. This is standardized between all vehicles, and you can buy your own OBDII reader for less than $70 (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=46030) - this particular one only reads the code numbers, and you'd need to find a website to list what the codes mean for your particular model.
Even better: You can get the codes read for free at any Advance Auto Parts or Autozone store. From their websites' Store Locator functions, it seems that there's one of each about 4 miles from you on Lorain Rd in North Olmstead.

3. On every vehicle I've ever owned, the CEL will shut off if the problem is repaired and then you disconnect the battery for a few hours. Actually, just unplugging the battery long enough on many vehicles will make the CEL shut off for a bit... It basically clears the codes out of the computer by starving the computer of power - just like clearing CMOS actually. However, if the problem still exists, the CEL will come back on after the computer notices it.

4. The Oxygen Sensor - this is a part which determines your fuel/air ratio. It really does make a difference in both gas mileage and emissions. If you've noticed poor gas mileage lately, this is probably the culprit. Getting one of the parts stores to read the codes will tell you for sure.
There are two O2 sensors on most 4-cylinder vehicles (is yours a 4-cyl or 6?). One should be a cinch to change, the other is a little more of a challenge. The easy one is usually located right in the middle of your exhaust manifold (it looks a lot like a spark plug with a wire tail) and it unbolts with a deep socket. You'll probably need some penetrating lubricant, like liquid wrench or WD-40 to get it unstuck, as they're usually slightly rusted in. This O2 sensor usually costs about $25 from the auto parts store. The other O2 sensor is usually about $100 to buy, because it's a more complex part. It's a self-heated unit that is usually located at or near the catalytic converter, bolted in just like the other one. These ones are heated, because for some perverse reason, the exhaust gases are no longer hot enough for the O2 sensor to get accurate readings that far back in the exhaust system. I've never personally had to change one of these, so I can't give much more guidance on that. I'd say, if it is the O2 sensor, hopefully it's the other one! ;)

Once you get your codes read out at one of those auto parts stores, please post back and hopefully we can give you more advice.

[csimon]

They want $350 at the dealer to replace my oxygen sensor ...I'm sure I can do it myself for far less. At any rate I've been having a simular issue for a few years now.
Pep Boys did the diag for free btw.

[madmat]

Unplug the ECM fuse for 2 minutes then replace it and it should reset the light. Barring that working just disconnect the ground on your battery for a bit.

[Gargoyle]

Even better: You can get the codes read for free at any Advance Auto Parts or Autozone store. From their websites' Store Locator functions, it seems that there's one of each about 4 miles from you on Lorain Rd in North Olmstead.

I've done this before, and it was a big help :thumbsup:

They want $350 at the dealer to replace my oxygen sensor ...I'm sure I can do it myself for far less. At any rate I've been having a simular issue for a few years now.
Pep Boys did the diag for free btw.

I replaced mine on my Camry for cheap, and the only reason it took me an hour is because everything is totally shoehorned under the hood, and I'm just not that flexible. That, and I didn't let the exhaust cool down enough before I started, and it took me awhile to realize that I could either keep burning myself, or I could let it cool off. :doh:

The procedure is easy, though.

[MountainDew]

If all else fails... black elecrical tape over the light does the trick.

[TheSmJ]

Most of the mechanic stores here will connect a scan tool to your car and read the code for free. I was at Autozone the other day doing this because of a cylinder misfire. I figured out it was a loose sparkplug cable and the problem vanished.

[Nosferatu]

My girlfriend just bought a used 1998 Mazda Protege a couple weeks ago. I believe it has a little over 120k miles on it. Just a few days after she bought it the CEL came on. Based on research I did before she bought the car, it's likely the gas gap isn't tight enough. She swears up and down it's tightened and the CEL stays on. So i'll see if she wants to take it to an AutoZone this weekend and get the code read, she'll definitely appreciate that it's free :). Thanks for the advice, i'll post an update when we do this. Hopefully it's nothing major, she needs to just have a reliable car for once. Her last car was a 1979 Mercury Marquis with problem after problem. :werr:

[profdlp]

JOY! JOY! JOY! :D

I woke up this morning
Ba-duh-duh-da-DUM
Put my keys in my hand
Ba-duh-duh-da-DUM
Went out to my ride wit'
Ba-duh-duh-da-DUM
The Short-Media Plan

{Crummy Harmonica Solo}

I yanked off the cable
Ba-duh-duh-da-DUM
To my batt-er-y
Ba-duh-duh-da-DUM
Then I was jukin' and jivin'
Ba-duh-duh-da-DUM
'Cause no light could I see

{More Crummy Harmonica}

Now they won't get my money
Ba-duh-duh-da-DUM
They can't do me wrong
Ba-duh-duh-da-DUM
For repairs I don't need, yeah
Ba-duh-duh-da-DUM
Now my blues are all gone

{Ineptly Played Guitar Solo To Fadeout}

:cool: :cool: :cool: :cool: :cool: :cool: :cool: :cool: :cool: :cool:

Thanks for all the help, guys. I'm filing all your advice away for future reference. :respect:

PS: MountainDew, I would not lie - had nothing else worked I'd have given the electrical tape a shot. :vimp:

[GHoosdum]

You should be a musician, prof.

[Buddy J]

Prof. Just to add, it would be worthwhile to get an OBD II scanner. Last I checked, you can get a good one for $35 at Walmart that comes with a CD listing the error codes for most vehicles.

It will read your codes and clear any errors your computer may be throwing with the push of a button. Comes in handy for diagnosing general auto problems.

Unplugging the battery worked and it cleared the error, but most likely, that light will come on again in the near future. You need to find out what error code is being given so you can rectify the problem instead of just masking it.

[a2jfreak]

I know on my Dodge Ram I can turn the key back, then forward (not to crank, but the click just before crank), then back, then forward, then back, then forward. (It might be forward, back, forward, back, forward.) Doing that brings up the OBDII error codes where the mileage normally is displayed. Once you get the codes you can look them up on the Internet. To reset the codes, just disconnect your battery for a few minutes (I've read anywhere from 15-30 minutes). Now see if the codes come back on w/in a short while. If they do, you probably have a problem. If they don't, it was probably something simple like a loose gas cap or perhaps a bad tank of gas.

[profdlp]

BJ & A2J: I strongly suspect that the sole reason for the light coming on at all was the factory-programmed reminder to change the PCV Valve at 60K miles. (Which was taken care of immediately.)

The fact that my gas mileage is still excellent (I made an 800-Mile round-trip to Virginia two weeks ago and averaged over 30 mpg, virtually the same as when the car was new), and that the car has passed an emissions test every year with flying colors leads me to think there is no "real" problem here.

Time will tell, and I won't really be 100% sure until several months have passed without incident.