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Don’t Ignore Your Check Engine Light: How to Handle It

The check engine light means one of your car’s systems is malfunctioning. If it’s flashing, pull over as soon as you safely can. If it’s steady, follow these simple steps.
April 4, 2018
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When the check engine light appears on your dashboard, your first question is probably “How serious is this?” And then, “How do I fix it — and how much will it cost?”

The check engine light is “your car’s way of trying to talk to you,” says Kristin Brocoff, spokesperson for CarMD, which provides information and products to diagnose car issues.

But the problem could be as minor as a loose gas cap, or more serious, such as a faulty oxygen sensor, explains Michael Calkins, manager of technical services for AAA.

Here’s what you should know about the check engine light and the possible problems it might indicate.

What the check engine light means

Solving check engine light problems

Check engine light codes

Common causes and repair costs

Resetting your check engine light

What the check engine light means

Sensors in your engine monitor the operation of its various systems and connect to what’s called the On-Board Diagnostic II (OBD-II) system. (Note that pre-1996 cars have an older version of the diagnostic system.) When something isn’t functioning properly, the check engine light appears to alert you.

A blinking or flashing check engine light indicates a more serious problem.

Engine lights may differ from one carmaker to the next. The light is either orange, yellow or red and is the outline of a car’s engine, sometimes along with the words “check engine.”

There are two types of warnings.

  • Check engine light on: If the symbol appears and stays on steadily, it could be a wide range of problems. It should be taken to a repair garage soon, Calkins says.
  • Check engine light flashing: If the symbol is blinking or flashing, this is a more serious problem. In these cases, Calkins says, you should pull over at a safe location, shut off the engine and have the car towed to a repair facility for diagnosis.

Some people confuse the service light with the check engine light, says Brocoff. However, the service light, sometimes in the shape of a wrench or the words “service now” or “service soon,” is only telling you that it’s time for regularly scheduled maintenance, not a mechanical problem.

Solving check engine light problems

The first step is to read the code provided by the car’s computer system.

The first step is to read the check engine light code provided by the car’s computer system. This is the information that’s been logged by the sensors in your engine. It can be read with OBD II scanners or readers through a connection (OBD port) usually located under the steering column.

To read the code you have three options:

1. Take your car to a mechanic and pay a diagnostic fee. Often, the fee is waived if you agree to have the necessary service performed at that garage.

2. Bring your car to an auto parts store and have the code read for free. The free check engine light diagnosis is good because if the code turns out to be for something minor, you might even be able to fix it yourself.

3. Buy an inexpensive scanner and read the code yourself. This is a particularly good option if you have an older car that might occasionally be showing a check engine light for minor problems. Scanners cost as little as $15, and some will wirelessly send information to your mobile phone.

Check engine light codes

Once you get the code, you still have to find out what it means. Type the code into a search engine, along with your car’s year, make and model, and you’ll usually get a description of the problem and some suggested repairs.

You can check the code online, but that alone may not tell you exactly what’s wrong.

However, simply getting the code doesn’t always tell you exactly what the problem is, Calkins says. It could put you in the general area of the malfunction, but further diagnosis is often required.

For example, a common check engine code is P0440. This code means that vapors from your fuel tank are leaking into the atmosphere, usually because the gas cap is loose. The fix: Tighten or replace the gas cap. In some cases, after tightening the gas cap, the light will simply go off after several days of driving. If it doesn’t, there may be other reasons for the leak.

Common check engine light causes, repair costs

The costs to fix whatever’s ailing your car and causing the light to come on can vary greatly. Repair costs for the most common check engine light problems range from under $20 to almost $1,200, according to CarMD’s analysis of millions of repairs recommended in 2016 in the U.S.

Here are the five most common check engine light problems and the repairs and average costs to fix them.

ProblemRepairAvg. total cost
(parts and labor)
Source: CarMD’s 2017 Vehicle Health Index
*Original equipment manufacturer
Faulty oxygen sensorReplace oxygen sensor(s)$259
Catalytic converterReplace with new (OEM) catalytic converter(s)$1,190
Ignition coil and spark plug(s)Replace ignition coil(s) and spark plug(s)$401
Loose fuel capInspect; tighten or replace as necessary$17
Mass air flow sensorReplace mass air flow sensor$378

» MOREHow much routine maintenance costs

Resetting your check engine light

With a code reader you might find you can simply turn off the check engine light yourself. However, if you haven’t fixed the problem, it will eventually come on again.

And if emissions tests or inspections are required in your state, a check engine light will make the car automatically fail. In some cars, the code is stored in the computer system, even if the light isn’t illuminated.

Besides that, “If you ignore the problem for too long it will have a snowball effect,” Brocoff says. What may start as a spark plug malfunction, which is relatively inexpensive to fix, could if ignored eventually damage the catalytic converter — a costly part to replace.

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