Why Did My Car's Check Engine Light Come On?

Leave a Comment - 27


Leda Lyons

Subject: Pt Crusier

Just had tune up the engine light came on then we were using the air the engine light
started flashing and dinging.We shut the air off the light flashing stopped but engine light is still on. What could be wrong?

gary mellis

Subject: check engine light on

computer code is transmission selenoid shifter, however, car runs fine---problem is it cannot pass inspection with check engine light on----even though code has nothing to do with emmissions. suggestions abyone?

Julie Perez

Subject: Annoying putt putt

I have a 2008 Pt cruiser, I had oil change, tune-up done and now the check engine light is coming on and my car starts to putt putt when I accelerate. I had my catalytic converter replaced and thought that would help the situation but no it's still acting stupid! Could this be happening if the gas cap is not good? When I took to emissions it passed but they gave me a new gas cap, now it's starting to act up. When I ran diagnostics it came up the catalytic converter was the issue code. I am so frustrated and hate to pay more money for something minor. Do you think it's worth me getting a new gas cap?

William A Randolph Jr

Subject: check engine lights

I have a 1994 oldsmobile cutlass supreme s and I'am having the same issue,tried everything short of a tune up.I replaced my locking gas cap and worked fro awhile,but it's coming back and no one seems to find a problem I had the codes taken off,but it just came back on,so now I'am really at a lost.I always start with a simple things frist and a gas cap is one.Buy a locking gas cap and see if that would help.I did found out that gas caps do go bad cause they don't hold a tight seal when they are old.


Subject: P0420

Check engine light came on car is running fine ,went to the shop they told me it was air fuel ratio sensor,got it replaced 2 days later light comes on again.I take it Monday to the same shop and now they tell me it's my C. Converter. In a matter of 5 days the shop changes,there diagnosis.

Gary Uhlman

Subject: P0420

As a professional Technician of 35 years it bothers me to see misinformation on the internet like in this article. It was stated that "With a code reader, you can pull the code to find out the precise cause of the problem." this is the biggest misconception by consumers and the author of this article. A p0420 is a Catalytic Convertor Efficiency code. The problem could be an oxygen sensor, catalytic convertor, wiring in the circuit or a bad PCM. A faulty Catalytic Convertor could be caused by a deeper rooted problem like excessive fuel causing the convertor to melt down or excessive oil consumption fouling the inside of the convertor.

The technician that checked your vehicle probably didn't take the time to provide a thorough diagnostic on your vehicle, hopefully you did not pay for his diagnostic skills or lack of. On the other hand, all to often customers do not want to pay for a diagnostic service. Day in and day out I hear "I've been to A***Z*** and they pulled my codes for free, I don't want to pay for a diagnostic, I know whats wrong with my car."

Accurate diagnostics require professional diagnostic equipment and an experienced, trained Technician. Ask around your community for a reference for a good technician. Be aware that good diagnostic equipment may be in excess of $10,000 dollars. Annual software updates can exceed $1,000 and a GOOD technician will not be the lowest paid person in the shop. The business will have overhead and needs to make a profit to exist. Be prepared to spend $100-200 for a good diagnostic. Remember that is money well spent compared to hearing "well now you need...."

Hope this information is helpful


Subject: Sputtering

I have a 95 bonneville and i replaced the maf sensor the check engine light is on and the car sputters what could be causeing rhis

William A Randolph Jr

Subject: check engine light comes on

I have a 1994 Olds Cutlass Supreme S,3.1.My check engine light comes on when I reach a speed over 40mph..Changed oil,all flud is ok,and gas cap is ok,as far as I can tell.Had another engine put in 2 years ago.Had a tune-up,new wires and plugs a few years ago.I had this issue eversince I brought the car back in 2003 and no-ne can find anything wrong and AUtozone donn't have an OB1 SCANNER.What can I do

Patricia Armstrong

Subject: check engine light

My check engine light just starting coming on, I have to take the emission test by the end of may. I checked my gas cap and when I opened it heard a small escape of air, does this mean my gas cap is bad? And really black electric tape r u kidding me, LOL

Carol Smith

Subject: check the engine light

Can be just adding a new gas cap. Mine does it about every 6 months and I change the cap. After I drive for awhile it goes out. Sometimes I just need to unscrew the cap and then screw it back in. Making sure it threads correctly.

kasozi Davis

Subject: Engine check

thx 4 your ideas but when I start my car, the engine check goes off and I can drive almost 300 km but when I stop for few five minutes when the engine is on, the Engine check comes on. what might be a problem?
Can a linkage (top cover seal) cause a problem to engine check

Merita curry

Subject: Car problems

I gave a warranty on my 07 Monte Carlo as and my car is have problems but every time I take it to the dealer they say there's no problem and tell me there's other things wrong please help.


Subject: Inspection machine in Paramus NJ illuminated check engine light

1996 well-kept Mercedes was taken for inspection. The check engine light was off. When it came through inspection, the light was on and the car was failed. Turning the key off and on reset the light. After a discussion with the techs, we decided I'd drive it for 15 min, then come back and run through inspection again.

The light was off. They plugged in their machine, and the light switched on. Amazing. One tech went to get a supervisor. We turned the key off and back on while it was still plugged in, so technically 'it passed'.

I have the sticker, but we witnessed the machine turn on the check engine light three times.

The techs were good to work with me as we tested the machine. Either the machine is broken, or there is something very strange wrong with the vehicle.


Linda C.

Subject: My check engine light never stays off

I've had 2 new catalitic converters put on, a solenoid, revap purge regulator, a bank 2 oxygen sensor and a new factor gas cap, but my check engine light never stays off. The code is P0441. I've had repairs done by different mechanics. Is it the mechanics or my car?? I'm at a loss. My car is not going to pass inspection once again and I'm afraid to pay more money for a repair that won't work again. Any suggestions?


Subject: If your car is running fine

If your car is running fine and smooth and your gas cap is on tight ignore that light as most of the things that set it off have nothing to do with the actual performance of your engine.
Most of it is crap from the smog emmissions in your tail pipe.
The dealers love it, as they can sell you a bunch of parts and labor.
If your car does not have to be smog checked to register it forget it.


Subject: If your car is running fine

Ignoring the light can lead to serious and catastrophic failure. If it is a problem with the oxygen sensors ignoring the problem inspection or not can lead to your catalytic converter failing. And like it or not this can lead to serious and expensive problems elsewhere in your vehicle. It costs nothing to have the light checked at any auto parts store. Do your self a favor and check it out.

Shawn Goldthwaite

Subject: Check Engine Light

Using a code reader to pull the check engine light code will point you in a direction to look, but it will not tell you precisely what is wrong with your vehicle. In most cases, you will have to have it diagnosed by a competent mechanic. For Instance, you may get a code for a catalytic converter inefficiency which may turn out to be a bad O2 sensor. Also, while spark plugs used to be a fairly easy inexpensive fix, most newer cars require more expensive plugs and may be located in the least-desirable places (ie under the intake). In most cases, I would recommend taking your vehicle to a qualified mechanic.

Gary Koerner

Subject: Engine light on vehicles - what to do

A no cost option is to call a national auto parts store, to see if they offer free testing, using a diagnostic tester (OBD II). You can also purchase an adapter which plugs into your car's OBD II port (usually found under the dash, near the steering wheel) which connects to your laptop computer's USB port. The software comes with the cord, and I paid about $30 for mine, including shipping. You can easily search the internet for more information on OBDII readers and adapters for your PC. It won't fix the problem or make you a mechanic, but you won't have to rely solely on the explanation of the problem which is given to you by your local mechanic or dealership.

Ryan Comeau

Subject: Check engine light resetting

Even though draining the battery of your car shuts the check engine light off it doesn't make the problem go away because when you drain the battery and then Try to get a sticker on the vehicle the vehicle will not pass. Although the light is off and you've cleared the memory you cannot beat the system because draining the battery sets all the computers monitors to not ready and the inspection machine picks up on that and the car will get a rejection sticker. Same thing happens when you shut the light off with a code reader.
So think twice about draining or disconnecting the battery or using a code reader to get rid of the light because the problem is still there so isn't the light. Get it fixed the proper way.

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Hi, i worked in the automoble field for 8 years, I was the CIO of a large 8 location dealer group.


 Frankly, i would be leary of doing business with a company that is still pushing paint protectant or undercoating.  Undercoating is BIG no no as it will actually cause rust.  It traps water between the steel and the undercoating causing corrosion, it plugs up the door and rocker panel drains as well as drain holes in the uni-body frame rails.  The dealers cost for the undercoating is about 250.00 including man hours, it is a huge profit booster and nothing more.  Although Paint Protectant will cause no damage, it does no good.  It is nothing more than an acrylic polymer protectant which can be purchased at an automotive store...cost for the dealer including man hours, 75-100 dollars.  It is nothing more than a profit booster.


 Gap insurance is worth it, if you are involved in a collision and your car is a total loss, the insurance company generally pays you the trade value for the car.  Gap insurance will pay the difference between what the insurance pays you and how much you owe on the car.  for instance, if the insurance company pays you 2k dollars and you owe 3k, the gap insurance will pay the difference of 1k.  However, if you are finanacing 75 percent of the vehicle cost, then gap is not needed.


  Here is my best advice, pay for the car and not a single additional item.  Pay no more than 10 percent over cost, ask to see the dealer invoice, add 10 percent and pay that price.  Gap insurance can be purchased through the finance company after the purchase.


 So, if the invoice states the car cost the dealer 20k, you offer 22k and not a dime more as that is a fair profit for the dealer.  Puschase no other add ons, none.  If they wont show you the invoice, there are plenty of honest dealers that will.  I would be very careful with this dealer.


 Dealers also make money on financing.  for instance, they submit your loan for approval, the bank comes back and approves the loan at 6 percent interest.  The dealer will add 2 or 3 points charging 8-9 percent interest and the dealer gets the money for the points at the time of sale. Ask them how may points they are adding to the bank rate.


 I summary, be careful.  dont fall in love as there are many dealers with the same car.  Offer 10 percent over the dealer invoice and purchase nothing else.  if the dealer gets defensive, fails to show you the invoice, or pulls other sneaky tactics...WALK.  go to another dealer.


 I strongly recommend visiting visit www.edmonds.com to find the dealer cost for your car as well as many other informative car buying tips.




If it is the original timing belt, then yes - check your owners manual for the recommended changing frequency, but from a quick web search (not knowing your exact engine model) it looks like 60,000 recommended internal, and typically last 80-100,000 miles to failure if not changed.

The most frequent comment (and a red note items on manufacturer's website) is that you probably have a "zero-clearance" engine, an idiotic design that means if the valves are not fully closed when the piston come to the top, it hits the valves and breaks or bends them or punches a hole in the top of the piston. Talk about planned obsolescence !

In short, if that is the case and your belt breaks or gets so loose it strips the "teth" off it or slips, your valve timing will be off, and could cause catastrophic engine damage that would require a complete engine overhaul or replacement !

Unfortunately, after looking at a video on how to change the belt, they build it so almost all the auxiliary equipment has to be taken off to change the belt - the alternator, water pump, radiator upper hose, power steering pump, air conditioner, etc - so rough cost is $800-1200 ! If you are getting it changed, it is also recommended to replace the water pump while it is off.

Hopefully some Montero mechanic will hop on this question and expand on this, but NO engine belt of any type should be trusted to go 115K miles.

A great deal depends on the use of the vehicle.  If you do a lot of mountain driving or heave towing, then a flush would be necessary.  Under normal driving conditions, a flush is NOT necessary at 46K miles.  The shops make money on flushes, that's why they recommend them.  Most transmissions are good for 100,000 miles before requiring maintenance.  Your owners manual should say.....if not then leave it alone.  Maintenance is debated between a flush and a fluid drain and fill.  Both have merits and down sides.  Alternative Car Care is not a fan of flushes and will not do them.  We would rather drain the fluid and change the filter.

Assuming automatic transmission:

At a quick lube type place, with unknown brand of fluid - from about $30-60 depending if done as part of a general fluid change package or all by itself. If transmission fluid filters need replacing too (usually are changed with fluid change on an automatic transmission), more like $75-125 range.

At dealer, using OEM parts and fluid, about twice to triple that. Normal auto repair shop about halfway in between those two. One reason for higher price is they will not (if reputable) extract the old fluid through the dipstick tube and put in new - they will remove the pan or maintenance panel (which commonly has to be done fgor filter replacements) and clean the pan at a minimum regardless.

This assumes you do not need band or continuously variable shift friction surface replacement or adjustment, which can crank it up from $50-100 for band adjustment to several hundreds more for replacements.

Do NOT let some shop convince you to pay for a transmission flush - not only is it unnecessary, but usually uses contaminated fluid from other cars or harmful chemicals (sometimes even tap water or diesel fluid) and can seriously damage your transmission. If your transmission filters were not doing their job or you smoked your transmission fluid, the proper cure (assuming not bad enough to require transmission overhaul) is to change to new fluid and filters, then replace them again in a short time - typcially 50-250 miles recommended by manufacturers, to let the new fluid pick up the dirt and sludge and transport to the filters for cleaning.

IF manual transmission - from about $40-75 for one with drain pan and no filters, to as much as $200 range for one with filters that requires removing side panel to change filter and clean it out. Again, higher end at dealers.

My recommendation - ALWAYS require OEM fluids be used for all but engine oil - mixing brands and additives in equipment is just not a good idea, as they can react with each other and cause serious degradation of the lubricating properties, and even cause gel or sludge in the fluid. A transmission, transfer case, differential, etc should be able to run at least several hundred thousand miles without maintenance if you change the fluid as recommended and use only the same OEM fluids in it. The small amount you will save using cheap fluids is not worth the mega bucks to repair or replace a damaged unit. If you go to an auto shop, find out your required refill quantities and buy the fluids at the dealer and tell them to refill with those - just be sure to get enough to allow for a bit of spillage.