What It Means When a Check Engine Light Is On or Flashing
The check engine light is part of your car's on-board diagnostic (OBD) system. This system is operated by the electronic control module (ECM), which is your car's computer. In modern vehicles, the ECM controls almost every major electrical or electronic system and continually scans for out-of-range operating parameters as reported by numerous sensors and actuators.
For example, a sensor or actuator may detect a misfire, poor fuel injection, unusual output voltage to the secondary ignition system, erratic operation of the fuel pump, or any other condition that might affect engine performance or emissions. Your car's computer will first try to correct the problem or wait a number of cycles. When the computer can't correct the problem, and it doesn't correct itself, the OBD system will store a diagnostic trouble code (DTC) in memory. This triggers the check engine light.
Since the computer stores a specific trouble code identifying the particular malfunction, it is a way to help car technicians and owners determine the nature of a problem and potential system or component involved. With the right tools, it also helps you troubleshoot your vehicle whenever the engine light illuminates.
In this guide, you'll find out what type of problems turn on the check engine light, what it means when it flashes, how you can retrieve the trouble codes stored in your car's computer, and how to go about deciphering those codes to help you fix your vehicle.
The Top 5 Check Engine Light Causes
Check these first:
- Broken wires
- Torn vacuum hoses
- Loose vacuum hoses
- Loose electrical connections
- Engine mechanical problems
What the Check Engine Light Does
Since 1996, motor vehicles have been equipped with the OBD-II (second generation) diagnostic system, an enhanced and standardized version of the previous generation. The OBD system—as it relates to the check engine light—monitors and controls the amount of emissions produced during the operation of your car by constantly checking and correcting input values to the appropriate systems with the help of sensors and actuators, including:
- Engine coolant sensor
- Oxygen sensor
- Knock sensor
- Camshaft and crankshaft sensors
- Evaporative emissions (fuel vapors) sensor
- Air meter sensor
- Canister purge solenoid
- EGR solenoids
- Fuel injectors
- Fuel pump
- Idle air solenoid
- Idle speed motor
Whenever the computer detects an abnormal condition through one of these, it sets a DTC in memory and lets you know by illuminating the light.
What a Flashing Check Engine Light Means
Intermittent Flash
| Continuous Flash
|
---|---|
The light flashes only when the problem appears. Possible causes include loose connectors or broken wires that disconnect when car goes over bumps. Problem may not be critical.
| A critical problem has been detected. Causes may include fuel passing into exhaust manifold.
|
When a potential emissions-related problem warrants your attention, you'll see the light illuminate in one of three different patterns.
Intermittent
Sometimes, the problem comes and goes. This is referred to as an intermittent or soft failure and can cause the light to flash, stop flashing, and then start again. The problem appears only when certain conditions appear. For example, the loose connector or broken wire that keeps connecting and disconnecting when the vehicle travels over bumps or irregularities on the road, causing the light to turn on and off for periods at a time.
Continuous Illumination
Whenever a problem causes the light to come on and stay illuminated, a hard failure is present. A dirty or failed mass air flow (MAF) sensor, for instance, will remain out of its normal operating parameters and cause the check engine light to remain on until you clean or replace the sensor.
Continuous Flashing
When the check engine light flashes continuously, it means you have a critical problem that will cause serious damage if neglected. Usually, this originates in a misfire that allows fuel to pass into the exhaust manifold and down to the catalytic converter where high temperatures ignite the fuel. Eventually, this condition will damage the exhaust system or catalytic converter. You need to fix the problem soon before a minor repair turns into a major and expensive one.
The light will flash if the computer detects:
- Engine mechanical problems including worn parts.
- Fuel system problems.
- Bad injectors, regulator, or fuel pump.
- Increased emissions.
- Bad oxygen, EGR valve, or EVAP sensor.
- Vacuum leak, hose, or gasket problems.
- Actuators or sensors sending bad signal to computer.
- Computer malfunction.
- Electrical short in a monitored circuit.
- Electrical connection problems, corrosion, or broken wires.
Check Engine Light Codes
When the computer detects an abnormal condition, it will store a DTC in memory and turn on the check engine light to let you know of the situation. Let's say, for example, that the oxygen sensor in the exhaust system detects too much oxygen in the exhaust stream and sends this information to the computer.
The computer tries to rectify by injecting more fuel into the engine. However, if one or more fuel injectors fail to respond, the computer will detect the problem, store a trouble code, and turn on the light.
Manufacturers have standardized the codes across all 1996 and newer models. This means that a specific code will point to the same type of problem regardless of what make and model you own. This makes it easier to troubleshoot and fix your car.
Diagnostic codes contain alpha-numeric values. The configuration of a DTC begins with a single letter, followed by four digits. So, a typical trouble code looks like this: P0102.
- The first letter denotes the type of code. This could be a "P" (powertrain), "U" (wiring-network), "C" (chassis), or "B" (body). We're concerned with "P" codes here, since they relate to the check engine light.
- Next, you'll see a "0" or a "1" digit: A "0" means you are dealing with a generic OBD code found in most vehicles; a "1" means you have a code specific to your car make and model, better known as a manufacturer specific code.
- The next digit will tell you in which system the computer detected the problem. A "1," for example, means the problem originated in the fuel and air metering system.
- Finally, the last two digits identify the specific circuit or component involved and the nature of the problem. For example, a "02" means the computer detected low input in the mass air flow sensor circuit.
Retrieving Computer Codes
Once you see the check engine light illuminate on your dash panel, you can retrieve the trouble codes.
OBD-I Codes
On pre-1996 vehicles, you'll find different procedures to retrieve the codes. With some models, for example, you can use a code reader—available at most auto parts stores—or an analog voltmeter. Other models use the ignition key to cycle between the on and off positions a number of times to read the code blinking light on your dashboard. You'll find the particular procedure in the repair manual for your specific make and model. You can buy a manual at most auto parts stores or online.
OBD-II Codes
Retrieving codes from a second generation OBD system requires the use of a scan tool. Scan tools come in various degrees of sophistication. You can spend less than a hundred dollars or a few thousand dollars on one of these tools.
For most owners with cars equipped with OBD-II systems, $70 and $200 dollars will be within their budget to afford a scan tool good enough to retrieve most check engine light related trouble codes. You can buy quality, relatively inexpensive scan tools at most auto parts stores or online. Some will display the code and a brief description of the code. Others will only give you the code, but most come with their own instructions manual and a list of diagnostic codes and their definitions. Additionally, many websites will help you define the trouble code and give you additional help in translating the code into a troubleshooting procedure.
Still, you may not have to buy a scan tool to get the codes. Some auto parts stores will run a diagnostic on your car for free. They'll hook up the scanner to your car's computer and retrieve any stored DTCs their scanner can find.
Yet, as useful as DTCs are to troubleshoot car systems problems, you need to keep one thing in mind when working with codes: Your car's computer will only point toward the circuit or component involved in a potential problem and the type of problem it's dealing with. This means the codes don't give the whole picture. You still have to confirm the circuit or component has failed.
One of the main reasons is that a fault on a wire, hose or connector, for instance, can fool the computer—and you—into thinking that another component has failed.
Take, for example, a loose or torn vacuum hose leaking vacuum. The oxygen sensor will report to the computer that fuel rate is too lean. However, unable to adjust the fuel ratio, the computer will set a "dead oxygen sensor" trouble code instead. Obviously, replacing the sensor won't fix the problem. So you need to troubleshoot the oxygen sensor to verify that in fact the sensor has failed. Otherwise, you'll start replacing good components without actually fixing the problem.
Retrieving Trouble Codes
How to Reset the Check Engine Light
Once you've diagnosed and repaired the fault that caused the light to come on, you need to clear the trouble codes from the computer's memory. On older vehicle models, you disconnect the car battery for a few seconds to clear the codes from memory.
But don't use this procedure on newer models or you risk erasing the computer system adjustments as well.
Disconnecting the battery on some OBD-II systems will require the computer to relearn sensor inputs—for days or weeks—and adjust output parameters to configure a driving strategy for better engine performance. Also, you'll erase your radio and alarm settings. In the meantime, you may notice the engine not working quite "right." Besides, the ECM on some modern vehicles can keep trouble codes in memory for a few days even without battery power. Instead, on a 1996 or newer model, use the scan tool to reset the light.
Warning!
Disconnecting the battery on some OBD-II systems will erase the driving strategy from the computer's memory.
Whenever the Check Engine light on your dash panel comes on, try to find out the reason for it as soon as possible. Self-diagnostic systems have become more advanced, going beyond typical monitoring operations. Modern OBD systems not only report system problems, but also checks how efficiently a system and its components are working.
The computer will let you know when one of these components is about to fail, saving you some money and road headaches in the process if you take advantage of these features. Even more, when a potential failure can cause extensive damage, the OBD system will produce a flashing signal to help you avoid expensive repairs.
Test Your Knowledge!
view quiz statisticsThis article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
The check engine light of my vehicle is continually flashing. What does this mean?
Some raw fuel is reaching the catalytic converter and could damage it. You need to make this repair before you have to replace the cat.
Helpful 41About a couple of months ago my check engine light was on, and it was due to engine misfiring on all four cylinders. So I replaced the plugs and the ignition coils plus changed the oil and filter. But the light still stayed on. So now the light flashes and my car won’t accelerate and my engine is making a loud noise and moving a lot. What is the problem?
The check engine light is flashing because the catalytic converter could be damaged. There’s seems to be too much raw fuel going through he exhaust. One or more sensors may be sending faulty signals. Download the trouble codes and see if you can find some information that can point you to a specific component(s) or system.
Helpful 242009 Chrysler Town and Country- Engine light flashes after idling in drive for about 30 seconds, then turns solid once I begin driving. In the past, the engine light has been solid for quite some time, and every time I have the diagnostic code run, it comes back to my gas cap. Any thoughts as too why the light flashes while idling, but doesn't flash while driving. Raw fuel to the Catalytic converter?
The gas cap may be loose or damaged. Unburned fuel going to the catalytic converter is what causes the flashing light. This usually comes from misfires. You may want to check for a leaking injector that might be flooding a cylinder when the engine is off. During normal driving, the cylinder may not have a problem burning the injected fuel.
Helpful 1My engine light is blinking in my 2008 Ford Edge. What's the problem?
Usually, this means the computer is warning you about raw fuel reaching the catalytic converter. This could be a misfire issue, but you need to diagnose the problem first. Do it as soon as possible before serious damage is done to the cat.
Helpful 18what does the p0032 code mean?
This code points to the oxygen sensor (bank 1) in front of the catalytic converter. There could be a malfunction at the sensor, connector or circuit.
Helpful 15
© 2015 Dan Ferrell
Comments
Hello i have opel astra 98 1.6 it doesn't wanna start. As soon as i turn the key on it flashes engine light.
My check engine light stays on and when i drive it bucks allot whats the problem
I have a 2004 ford taurus and my check engine light in on all the time. It reads high voltage what can it be
My CEL has been lit for a long time. but recently, after a change of 2 coils, the CEL flashes intermittently - most times as i attempt to accelerate.
What could this mean?
car is a Toyota camry 2007 LE.
may code is P 0462 can you explain
MY RADIATOR IS LEAKING RIGHT AROUND THE LARGE BOLT ON THE RADIATOR WE RELACED THE RADIATOR AND TIGHTENED THE BOLT IT IS STILL LEAKING PROFUSELY. THE HOSE MAY GO INTO THE TRANSMISSION WHAT DO WE DO ?
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i JUST got a 2012 buick enclave v6 it was on the lot a while and the battery COMPLETELY drained Thursday morning and now wont crank i haven't even registered it yet.... what is my next move i paid in full no liens
My check engine light flashes when i try to accelerate faster and when you go up hills????
My CEL came on and someone used a scanner to check the code..then accidentally erased it i need it to come back on so the repair will be covered under warranty. How can i get it to come back on?
Hi.
My engine light came on last week. I called out lube mobile amd they detected the coul pack was the trouble. We replaced that ( didnt change the spark plugs at the time though we shouldve) and now a week later my engine light is back on again. Any ideas?
Eveytime i start my 2001 audi a8 the engine light will start flash and then stop but this time i was driving and the car died on me i change the camshaft sensor/fuel pump and the crankshaft senson and still nothing any ideas?
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My check engine light has flashed for just a few seconds twice in the last 3 months. Had firestone check codes and they said only thing that was reading was mass air flow error. Should I be worried? Is this a major problem?
my turn signal lights wont stop blinking and now it actually signals opposite when i need to turn for example if im Turning left and signal left it actually starts signalling right, but the thing is the computer itself was not diagnosed the first check up to see what the problem was and then when they ordered and put my signal arm part, is when they noticed my computer has burnt spot on it.
If the battery cable is loose will it make a knock sensor show up bad and make the check engine light come on?
Engine light (yellow)on. Last time it was about 2 weeks ago that came on and diapered after refuling.
fantastic platform, my car is flashing check engine light continuously immediately after an electrician worked on it and he said it is a code. can this be true?
My engine light is flashing
Hi I have a Kia Rio 4cylinder 2006 model. I've had spark plugs, timming belt ,radiator ect fixed when my timming belt went recently got a new battery and fullpump put in .car starts fine but today the engine light is flashing and losing power can it be the starter motor
Hi there Dan!,
My sisters 2002 Holden Astra is turning over but won’t start. Her check engine light is flashing and it sounds like her carbon canister valve is ticking?! Pls help.
TIA
Hi, my check engine light starting flashing today, mechanic said to bring it over in the morning, can I drive it to get to my mechanic who is 10 mins away.
my Octavia 2003 has auto G B .CHECK engine constantly illuminating.equippedwith bad shifting G B . i had replaced 3 times sensors GEAR BOX G38 &G68 .AFTER CARING ABOUT 500KM IT illuminates
Hai sir,I am in India,the Nilgiris. My opel astra 1998 model was didn't start no spark. The engine management light was blinking. I change ignition coil pack and wires and cranksensor. I need your help.
Hi Dan, my car won't gear up when hitting the highway. I accelerate but will stay around 40-50 mph. When this happens an intermediate check engine light appears. I can slow down and the car will jump into the next gear though. I drive a 2004 Grand Prix.
Any suggestions are appreciated!
Hi, My Honda Accord 2009 LX has a constant blinking check engine light on and i keep hearing a ticking sound from the engine. Also i noticed the car is not firing properly and the smoke from the exhaust is black . please what should i do to fix this.
Hi Dan thanks for your reply and input, suspect the same as you have mentioned and have checked most of the wiring harness and connections with no luck, no error codes with OBD scan. Since my post I checked again and as said lightly touched the wires to the indicator/high/low beam switch (Yellow/white wire this time) and since all is working fine again till next time, so far the engine check light comes on every time and starts fine even the throttle control valve is working fine now again which was a problem before. My suspicion is that there is a problem with one of the wires in the loom under the dash. Will only be able to check the wiring again when the problem comes back. As you say intermittent problems are very hard to trace, this one more so as I have to check continuity through each wire which could end up not being a true reading as by touchin the wire continuity could be found.
2002 Opel Corsa light 1.4, my problem is somewhat different though, when I switch car on and the engine check light comes on (it blinks) then the car will start, but then sometimes the light won't come on and the car won't start. To my thinking it must be a weak or bad connection somewhere because if I fiddle with the wiring it comes back on, sometime a light touch other time more vigorous, but as it goes never the same wiring loom or wire. How now, has anyone experienced this before.
So my check engine light was consistantly on but when I accelerate it started to flash but when I unhooked my mass air flow sensor it didn't flash any more
I drove into a bump then the engine light start to flash and the car started to jurk when I was going slow and there is a weird smell coming out of my truck. Avalanche 2005 1500. My husband changed the spark plugs and now the light stays on for a while then start to flash while driving. And still runs funny and have that smell.
My battery light is on engine light blinks car act like it stuck in high gear
Well, here's a new one for you. The engine light and stabilitrak/traction control lights came on after new spark plugs were installed. Engine was jerky (hesitation) and brakes did a pulse grab occasionally when applied. Error codes were P0171, P0174 and a G??? code for the Traction Control. Guess what?...the problem was not the air flow, oxygen or fuel system sensors or the fuel injectors or vacuum lines, etc., ...it was one of the new spark plugs (GM iridium?) that was faulty. How about that! New plug replaced, running like silk. The vehicle is a Saturn Outlook 2007 with 135,000 Km that is in showroom condition. Always well looked after. Hope this helps.
My 1996 Prado speedometer and odometer stopped working. When the speed increa, the O/D Off light started blinking on the dashboard. I did the manual diagnostic using a jumper inserted between TE1 and E1. The check engine light continuously blinking steadily. What does it mean?
Check engine light will blink for several minutes or stay on. I have used a code checker but it will not show a code, just blink as long as the checker is plugged in. 2000 chevy silverado 1500 5.3.
This write-up has been very informative. it is written so even dummies like me can have a little knowledge of what they're looking for. My trouble where my vacuum lines were Rotted .Thank You AxleAddict.
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