Q: What is the check engine light?
A: The check engine light or "Malfunction Indicator Lamp" (or MIL as it is called today) is supposed to alert the driver when a problem occurs in the engine control system. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash. Some types of intermittent problems will make the lamp come on only while the fault is occurring. When the problem goes away, the lamp goes off. Other types of problems will turn the light on, and it will remain on until the fault is diagnosed and repaired.
Since the earliest days of full-blown computerized engine-control systems, there has always been some type of built-in self-diagnostic capability to detect faults. A computerized engine control system uses inputs from a wide variety of sensors and switches to regulate spark timing, fuel delivery and other emission functions. If a sensor fails, reads outside its normal range of values or can't send its input back to the computer because of an open or shorted circuit, it can alter engine performance and emissions.
The computer has to have accurate inputs to make the right commands and keep things running smoothly. Likewise, the computer has to be able to carry out its command functions and send its instructions to the ignition module, fuel injectors and other control devices. If the proper commands can't get through, that too will cause problems. Monitoring the operation of the various inputs and outputs is what on-board diagnostics is all about. When computerized engine controls went nationwide in 1981 to comply with federal emission regulations, the "Check Engine" light became a new feature on the instrument panel.
Today's emission testing uses a scan tool to check if the Check Engine lamp is on, and if the light has been tampered with and if this is the case they fail you. Whenever the Check Engine light comes on, a "diagnostic trouble code" (DTC) is also recorded in the on-board computer's memory that corresponds to the fault. Some problems can generate more than one fault code, and some vehicles may suffer from multiple problems that also set multiple codes.
What's included in our diagnostic service
- Check for active or stored fault codes
- Check potential contributory systems against manufacturer specifications, including fuel pressure, fluid levels, charging system.
- Check for pertinent Technical Service Bulletins (TSB's) as listed by the manufacturer
How Your Check Engine Light WorksPosted July 1, 2012 1:45 PM
Have you ever had an experience like this in Tucson? You're driving through one of those automatic car washes. When you get to the end, where the dryer is blowing, your check engine light starts flashing!
You fear the worst, but within a block or two, the light stopped flashing, but stayed on. By the next day, the light was off.
You wonder; "What was going on?" Well, it's actually a good lesson in how the Check Engine light works.
Your air intake system has a sensor that measures how much air is coming through it. When you went under the high-speed dryer, all that air was blasting past the sensor. Your engine computer was saying, there shouldn't be that much air when the engine is just idling. Something's wrong. Whatever's wrong could cause some serious engine damage.
Warning, warning! It flashes the check engine light, to alert you to take immediate action.
It stopped flashing because once you were out from under the dryer, the airflow returned to normal. Now the engine control computer says the danger is past, but I'm still concerned, I'll keep this light on for now.
Then the Check Engine Light goes off in a day or two.
The condition never did recur, so the computer says whatever it was, it's gone now. The danger is past, I'll turn that light off.
Now a flashing check engine light is serious. You need to get it into one of our locations as soon as possible. But if it stops flashing, you have time to see if the problem will clear itself or if you need to get it checked. How does the computer know when to clear itself?
Think of it this way. The engine control computer is the brain that can make adjustments to manage the engine. Things like alter the air to fuel mix, spark advance, and so on. The computer relies on a series of sensors to get the information it needs to make decisions on what to do.
The computer knows what readings are in a normal range for various conditions. Get out of range, and it logs a trouble code and lights up the check engine warning.
The computer will then try to make adjustments if it can. If the computer can't compensate for the problem, the check engine light stays on. The computer logs a trouble code.
Some people think the code will tell the technician exactly what's wrong. Actually, the code will tell the technician what circuit reading is out of parameters. It can't really tell you why, since any given circuit will have a number of relays, fuses, sensors, solenoids, valves, and wiring that can cause the circuit to malfunction.
Let's say you're feeling hot. You get your heat sensor out – a thermometer – put it under our tongue and in a minute or two you learn that you have a fever of 104 degrees.
You know your symptom – a fever – but you don't know what's causing it. Is it the flu, a sinus infection, or appendicitis?
You need more information than just that one sensor reading. But it does give you a place to start and narrows down the possible problems.
There are reports on the internet telling you that you can just go down to an auto parts store and get them to read your trouble code or buy a cheap scan tool to do it yourself.
There are two problems with that. First, the computer stores some trouble codes in short term memory, and some in permanent memory. Each manufacturer's computer stores generic trouble codes, but they also store codes that are specific to their brand.
A cheap, generic scan tool, like you can buy or that the auto parts store uses, doesn't have the ability to retrieve long-term storage or manufacturer specific codes. Your BRAKEmax service center has spent a lot of money on high-end scan tools and software to do a deep retrieval of information from your engine control computer.
The second problem is that once you've got the information, do you know what to do with it? For example, a very common trouble code comes up when the reading on the oxygen sensor is out of whack.
So the common solution is for the auto parts store to sell you a new oxygen sensor, which are not cheap, and send you off on your way. Now your oxygen sensor may indeed have been bad and needed replacing, but the error code could have come from any of a dozen of other problems.
How do you know the right solution? Back to the fever analogy, do you need surgery or an aspirin? Leave it to the pros at BRAKEmax Car Car Centers. Give us a call and let us help you resolve your check engine light issue.