Service Engine Soon Light On

What does it mean when the service engine soon light comes on in your can and how do I reset it? Learn what is wrong with your vehicle and how you can repair it from an experienced mechanic.

Car manufacturers install service engine soon lights into cars to simply let the car owner know that there is something that needs to be checked out on their car. There are many systems on your car that are monitored by your cars computer. When the computer notices a problem in one of these systems it will turn on this light to let the vehicle owner know that they need to take it to their mechanic.

Flashing service engine soon lights can be very confusing. What do they mean? Are they important? What should you do about them? How do you turn them off?

Drawing from my years of experience as a mechanic and questions that I get from my readers, I have listed the common problems and solutions below.

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Reasons Why Service Engine Soon Light Comes On

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Cylinder 1 Misfire, Service Engine Soon

I have a 2004 Mustang 3.8L V6. I have been having sputtering lately and the service engine soon light came on and blinked twice and then became solid.

I got the code checked and it was cly. 1 misfire. I have since replaced plugs/wires and added Seafoam just in case it was a dirty injector.

When I replaced the plugs/wires the sputter got much much better. It doesn't do it while driving now (it was before the change of plugs/wires). Now it only does it while idle like at a stop sign/red light or sitting still. It got a bit better after the Seafoam treatment too, but the light is still there and the sputter is still there. I also noticed my RPMs drop while I was rolling down my window (power windows).

This has me thinking that the problem is electrical and not mechanical. I have not done a compression test (do not know how/what exactly it is) and I am praying its not a head gasket. Please help!

Answer: Hi Jason. Thanks for asking me your question. There are many things that can cause a misfire. Since you have already replaced the spark plugs and wires that will help narrow it down. It could be a problem with a weak ignition coil for the #1 cylinder. It could also be an injector that is leaky or faulty. It is also possible that the compression is low on that cylinder.

Compression tests are fairly easy. Basically you remove all the spark plugs, then thread a compression tester into the cylinder you want to test then crank the engine and see what the gauge says. If it is low it is probably because of a valve problem or worn rings.

It is possible but unlikely that this problem is caused by a bad head gasket. If the head gasket is the culprit, there should be many other symptoms as well, with the main one being overheating.

Your service engine soon light will turn off after you get this problem fixed.

Vehicle Shakes, Service Engine Soon Light On

The service engine soon light in my car comes on and off and my car shakes a little. I thought It may need some balance or something. Why do you think my service light comes on and off? Other than a little shaking it seems to be running well. Thank you!

Answer: Hi, Sergio. Thanks for asking me your question. The most likely cause of your shaking and your service engine soon light is a cylinder misfire.

The first step is to figure out the trouble code with an OBD II scanner. Alternatively you can take your car to an auto parts store and they will be able to read the codes to you. Most of them provide this as a free service.

After you know the code you can come back to my website and do a search for it. There are many causes of misfires but some of the common ones that I see are spark plugs and/or wires, ignition coils, ignition control modules, low fuel pressure, faulty fuel injectors, etc. It will take some testing by a skilled technician to figure out why it is happening.

It is important to get this taken care of because all of the extra fuel going into the catalytic converter can cause it to go bad and they are usually fairly expensive.

OBD Code P1100, Service Engine Soon

What is code P1100 on a 1995 Chevy S10 pickup with the 4.3L motor?

Answer: This code is for the MAF or Mass Airflow Sensor. This is the definition for code p1100: P1100 MAF Intermittent.

The most likely cause of your service engine soon light is either a dirty MAF or loose wiring or connector. If you want to clean it just buy some contact cleaner and spray it onto the MAF wire. Be very careful as this wire is very fragile.

If this does not help then you will probably have to get some professional help as it could be a pretty tough diagnosis.

OBD Code P1105, Service Engine Soon

Back in November of last year, an auto mechanic changed the O2 condensor on my car. They had some problems getting to the part and making the change and said they thought they got it tight.

I have had problems since then. Now my car is missing badly and just last week an error code 1105, which is the fuel pressure selnoid. Also my service engine soon light is on. They said the O2 problem has nothing to do with this problem and refuse to check out the O2 condenser.

I plan to have someone else look at it, but need to know if a bad exhaust system would cause the code 1105 or if the O2 condensor isn't in right would this cause the problem. I don't want to replace the fuel pressure solnoid if it could be one of these. I haven't had the exhaust change since purchasing and understand (looking at website info) that the manifold has something to do with the fuel pressure solnoid.

Thanks, Karen (1998 Mitsubishi Eclipse GST)

Answer: Hi Karen! Thanks for asking me your question. This code can cause your service engine soon light to come on.

I'm not sure but I think you mean "02 Sensor". I have never heard of an 02 condenser. Either way, this sensor probably has nothing to do with the current code that you have because it is in a completely different system than the O2 sensors.

The code you are having is generated by the cars computer when it does not see the fuel pressure control solenoid valve working correctly. Most likely it is simply a problem with the solenoid and it needs replacing, but it could be other things like wiring or vacuum problems.

The exhaust manifold has nothing to do with the fuel pressure solenoid. However the intake manifold does because this is where the vacuum comes from that helps to operate the solenoid.

It is a good idea to have another shop check your car out just to be sure that this has nothing to do with the work that was previously done, but it sounds like it probably does not.

Sulfur Smell, Service Engine Soon Light

I have a 1997 Toyota 4runner 3.4 V6. My service engine soon light recently came on and my exhaust has been more pungent than normal. Also on occasion the car produces a sulfur (rotten egg) smell... Any ideas?

Answer: Thanks for asking me your question. There are quite a few things that can cause this type of problem. The first thing that you should do is have your codes read with an OBD II scanner. After you know what the codes are you will have a much better idea of what might be going on. You can also search for the code numbers on my website or on the internet to see what might be causing them.

The sulfur smell or rotten egg smell that you are getting is probably due to too much unburned fuel being put into your exhaust system. In other words your engine might be running rich. It is normal to smell this smell some as fuel has sulfur in it, but if you have not smelled it before and your check engine light is on then, there is most likely a problem somewhere.

Sometimes just the way you drive can cause more of a sulfur smell. If you drive a lot of short trips or do a lot of aggressive acceleration you might notice the rotten egg smell more. Some brands of gas have more sulfur than others too, so the type of fuel that you put in your car will also affect it.

I think once you get the code figured out and repair whatever is causing it your funny smell should go away as will your service engine soon light.

Service Engine Soon Light Comes On and Off

My car has a high idle, then it feels like it's going to stall and radio goes off then back on. I had diagnostic done but nothing has come up. The service engine soon light comes up then turns off. Any advice? (2002 Pontiac Firebird V6)

Answer: Thanks for asking me your question. If the service engine soon light has come on (even if it is off now) it will have set a code. This would be the first thing that I would check. The code that is set will give you and idea of what might be causing the problem.

I don't know who you had to the "diagnostic" but if they couldn't get the code then I question whether they knew what they were doing. Any time the engine light comes on there will be a code. Sometimes it will be stored in history, but it will be there unless there is a problem with the computer.

There are many, many things that can cause this problem. After you get the code with an OBD II scanner, you can search my site or the internet for the root causes.

Car Runs Fine, Service Engine Soon Light On

What is causing the check engine light to come on 2000 Ford Explorer Sport?

Answer: Thanks for asking me your question. The reason that your service engine soon light is on is because your computer has found a problem in one of the systems or circuits of your car.

Most auto parts stores and many repair shops will read the codes for free then you can come back to my website or search the internet to find out what the causes might be. Even though your car seems to be running fine, there could be something that is wrong that is causing damage. It is important that you know what is going on so you can repair it if needed.

Rough Idle, Random Misfire Code, Check Engine Soon

2001 Mitsubishi Eclipse-2.4L On a cold morning, it starts and idles at about 1300 for a few minutes til it's warmed up, then idles down to a 100 but doesn't stall out. Whilst driving it seems to run smooth til you stop, then the rpm needle bounces all over the place (only to go down to 100 again-car shakes like a leaf.) A few times, when pressing the gas pedal, it will rev up, but go no where or just jerk. :(

The dash says Service Engine Soon and it's thrown an EGR Valve code then a 'Random Misfire Code'. I have changed out the IAC already. Any advice would be greatly appreciated! :)

Answer: Thanks for asking me your idle question. The most likely cause of your problem is that the EGR valve is sticking open causing your car to misfire and have a really low idle. It is possible that it is other things, but this is the most likely cause.

Any good auto repair shop should be able to diagnose this problem without too much trouble. This would be hard to diagnose yourself but if you are good with cars and have the tools you probably could.

Cylinder 6 Misfire, Service Engine Soon

My truck has 120,000 miles. Cylinder #6 is misfiring every time. Service engine soon light is on. When I crank it, for the first few seconds, it sounds like it does not miss, then it starts missing and does not stop until I turn the motor off. I checked the compression at idle and it showed 60 psi. I also checked cylinder #2 and it showed about 65 psi at idle.

I also checked cylinder #2 and it showed about 65 psi at idle. I checked the spark and I am getting spark from every cylinder. I have 3 coil packs. I also switched the coil packs to see if one was putting less power out than the others and nothing changed. Also, when I had the compression tester on cylinder #6, after I was done checking the compression, I pushed in the release valve and smelled gas.

I have spark, gas, and compression. What could the problem be? (2003 Toyota Tundra 3.4 V6)

Answer: Thanks for asking me your question. The first thing you should do is re-check the compression. If you checked it with the truck running it would have given you incorrect readings. To do a compression test you need to make sure the engine is warm, then remove all of the spark plugs and coil packs. Then turn the engine over with the throttle wide open while reading your compression tester.

The reason that you need to redo this test is because your truck should have a MINIMUM of 145 PSI. Ideally it would be around 175 PSI. It should not have less than a 15 PSI difference between the cylinders.

After you do a compression test again if it is still low then squirt a few squirts of oil into the cylinders that are low and see if the reading comes up. If it does then it likely has very worn rings. If it does not then you are most likely looking at a valve problem. Your service engine soon light should go off after you get this repaired.

Service Engine Soon Light Comes On and Off Sometimes

2003 Jeep Grand Cherokee service engine soon light on and off periodically and sometimes dies at stop or idle.

Test says something about emissions. Mechanic replaced a part, (will have to look at bill to see what is was if you need to know to help solve problem) but still does it. The check engine light comes on for a while then may be off a day or so. Jeep dies once in a while at stops or idling. It is a 6 cylinder. I think my hubby calls it a straight six? Thanks beforehand.

Answer: Thanks for asking me your question. There are many things that can cause this type of problem and without knowing what the code was that was set there is really no way for me to narrow this down too much. It could be something related to the emissions or it could also be a problem with your idle air control (IAC) valve or circuit.

Judging from your description I'm guessing that the mechanic replaced the exhaust gas recirculation (EGR) valve hoping that it would fix the problem. This part can cause this type of problem, but it needs to be tested and diagnosed first to be sure that is what is causing it.

I would talk with the mechanic that did the work and tell them that you either want your money back since he didn't fix the problem that he said he would or a credit for diagnosing and fixing the actual problem. If he won't do it then it's time to find another mechanic.

Car Vibrates While Stopping and is Slow to Accelerate

My 2001 Ford Mustang, V6, 3.8L, (172,000 miles) vibrates when I'm stopped at red lights and slow to accelerate after stops. I have had a full tune up, new spark plugs and fuel system flush and check and still having problems. The light says Service Engine Soon. The code reader was a PO302, Cylinder 2 misfire and Cylinder 6 misfire.

The repair shop said that they could not help me, but thought it may be a broken head gasket. Is this a possibility or could it be the wrong spark plugs (Bosch brand)? I've heard that this brand does not work well with Fords. Help!

Answer: The first thing you need to do is find another repair shop...one that will actually do good work and care about their customers. If your car did not have this problem before you had the tune up then it is most likely something they messed up on.

The misfires are the reason for the vibration and low power. The most likely cause of these misfires are spark plug wires that were crossed or maybe not seated correctly (assuming they are the right ones for your car).

It is possible but very unlikely that your car has a head gasket problem (especially if it has never overheated) or any other major problems. I think you will find that it is probable a simple fix if you can find a good mechanic to look at it.

Service Engine Soon, Mechanic Can't Diagnose Problem

My 1999 Toyota Camry LE, 4 cylinder with 126,000 miles, the service engine soon light keeps coming on.

I've brought it to a very dependable and honest repair guy who I've used for years and he has, I'm told, the most expensive diagnostic machine out there. I've brought it there 3-4 times and after the last time he said that he can't find what the problem is & why the light keeps coming on. He hasn't charged me the last 2 times after he thought he fixed it (the 2nd time), so I know he's trying to do the right thing.

After a day or two, the service engine soon light goes off only to come back on another day or two later & stay on for a couple days. However, the car seems to be running fine. I'm wondering if it is just a short somewhere.

Is it worth trying to get a 2nd opinion? I'm loathe to bring it to a dealership to pay some of their exorbitant rates.

Answer: In my opinion it would be worth it to get a second opinion if your regular mechanic cannot fix it. You can do some checking yourself on the internet if you find out what the code is. I have quite a few codes listed on my website and there are a lot on other websites as well.

Some codes are very hard to trace down. It sounds like you have a good mechanic so I don't think he ripping you off, but if he can't figure this one out you will want to take it somewhere that can. I don't know how he would feel about it but you could even ask him if he knows anyone else that might be able to figure it out.

Sometimes dealerships have good diagnostic techs, but many times a really good independent shop is even better.

It is important to get this repaired even though your car is running fine. The computer has noticed a problem, and most of the time these problems will be causing some type of damage even it is seems to be running well.

OBD Code P0325, Car Skips and Bucks

My 2000 Nissan Xterra has a bad misfire when it gets warm. While it is cold it seems to be O.K. but gets progressively worse as its warming up. There is no service engine soon light on. When it's running and hot it bucks badly.

There is a P0325 code pending which I thought was a result of the bucking and the misfiring. Even after I clear the codes the 0325 code will come back, I can't see the knock sensor causing the bucking and skipping. The truck has 145,000 miles on it and has been well cared for.

I installed a new set of spark plug wires thinking it might be a bad wire. A friend told me his Nissan pick up truck was doing the same thing and said that I needed to replace the distributor. The engine is a 3.3 V6 with an automatic trans and 4x4. Thanks for any help. Jim

Answer: The computer uses the knock sensor to tell when your engine knocks. If it does then the computer will change ignition timing to make it so it does not knock. If the knock sensor was malfunctioning and sending the wrong signal to the computer then the computer might be drastically changing the timing which could account for your driveability problems.

Code P0325 will not ever go away even if you turn the service engine soon light off because it is a constant fault. The computer will test the knock sensor circuit often and will set code P0325 until the problem gets fixed.

The computer will not necessarily turn the check engine light on with this code because it does not know that the signal is bad. It simply thinks that there is a knock because of what the sensor is telling it.

Most likely this is just a bad sensor, but it could also be a problem with the wiring for the sensor circuit.

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