Check Engine Light - Should I Pull Over or Can I Keep Driving?

Updated on October 6, 2019
Ian Mundell profile image

Ian is a car enthusiast who's driven cars, motorcycles, and trucks all over the world and still loves to drive a manual transmission car.

It’s no secret that today’s cars are heavily controlled by computers. In modern vehicles, computers regulate almost everything including ignition timing, fuel mixture, transmission operations, and a whole slew of other details.

A car’s computers have become extremely sophisticated, and part of that sophistication is the ability to deliver detailed information to the driver about any potential problems. Most of the time, the computer can detect common problems and relay the necessary warnings via dashboard lights or messages on the car’s screen.

You might’ve seen some of these warnings: low pressure in a tire is signaled with a Tire Pressure Monitoring System (TPMS) light, for example.

But sometimes a car will have a problem which fits into an annoying category. The computer can detect a problem and is programmed to know it needs to show a warning, but the computer either:

  • can’t fix it automatically; or
  • thinks it’s too complicated to pin down to a specific problem; or
  • has detected a serious issue that needs immediate attention.

In this article I’ll discuss some of the most common causes of a check engine light, and look at some ways you might be able to fix the problem yourself (even if you know nothing about cars). I’ll also cover the two types of check engine light warnings and why one needs more urgent attention than the other.

Two Types of Check Engine Light – Solid and Flashing

You may not have known that a check engine light can be either solid or flashing. But one of these is much more urgent than the other.

Flashing – Pull Over and Call for a Tow

This is a message you definitely should not ignore. A flashing check engine light indicates a serious problem that could result in very expensive damage to your vehicle. One of the most common problems this indicates is a severe misfire or other engine problem, such as fuel being spilled into the engine exhaust system.

That can be problematic for all kinds of reasons. The car will typically be very rough driving, and could stall. You can expect drastically reduced efficiency and much higher costs at the gas pump.

But the most severe potential problem is damage to the car’s catalytic converter. This is a crucial part of the exhaust system which reduces dangerous chemicals that otherwise would be blasted out into the air. If it’s not functioning properly, your car won’t be able to pass an inspection in most states.

Worst of all, a catalytic converter replacement is very expensive. For a typical family vehicle the cost of replacement (including labor) is between $900 and $3000. It’s a complicated maintenance task, and it should be done by a professional with a full shop and proper safety equipment. Replacement involves lifting up the car and cutting into the exhaust system with a power saw, as well as potentially welding a new converter in place.

Replacement Catalytic Converter
Replacement Catalytic Converter

Other Symptoms of a Failing Catalytic Converter

Besides a check engine light, be aware of a rattle from the catalytic converter when the car is idling. (If you notice a rattle at idling, but can’t tell where it’s coming from, ask your mechanic.) The other common symptom is a bad smell from the car’s exhaust pipe (it’ll smell like rotten eggs).

Solid - Usually Safe to Drive

A solid check engine light is much less serious than a flashing light, and you can drive for a while without fear of causing expensive damage to your car. It still needs to be checked out, but there are some things you can do that might fix the problem.

Check the Fuel Cap

A loose or damaged fuel cap can result in a check engine light. Modern vehicles have a clicking fuel cap which provides an audible noise when it’s properly tightened. If the fuel cap is missing or damaged, you can buy a replacement for as little as $5. But it may take a while for the sensors to reset properly and the light to go off.

If you have a Ford that’s 2008 or later, it probably has a capless system. If you get a check engine light and your car doesn’t have a fuel cap, you’ll need to get a diagnosis to find the problem.

Other Causes of a Check Engine Light

The other most common causes for the check engine light to illuminate are bad sensors.

The oxygen sensor, or O2 sensor, is used by the car’s computer to check the engine's air-fuel mixture. A replacement will cost between $80 and $150.

The mass airflow sensor (MAF) will tell the car’s computer how much air is entering the engine. This is also important for the computer to know how to adjust the fuel being sent to the engine so it can maximize efficiency.

How to Check Engine Codes

Mechanics can get a great deal of information from the car’s computers, and a significant error (the kind that will trigger the check engine light) will be stored in memory for the mechanic to look up later. Any vehicle built in the last 20 years has a plug underneath the dashboard which is called the OBD-II port. OBD stands for On Board Diagnostics, and OBD-II is a standard which can be read by any scanner that knows the codes.

You can buy an OBD-II scanner for as little as $30 at Amazon. You’ll be able to then plug it into the proper port in your car and read the codes stored in the computer’s memory. Most of them are standard, and it’s easy to search online to find what a particular code means for your specific car.

Don’t Ignore a Check Engine Light

A check engine light means your car has a problem and the computer is giving you a warning. If it’s flashing, it’s urgent and you need to get it checked out immediately. If it’s solid, try checking the fuel cap, especially if the light comes on shortly after you’ve visited the gas station. Keeping up with maintenance is the best way to protect against an expensive repair being needed. Get a proper diagnosis as early as you can, and find out what your car is trying to tell you.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

  • What could cause the check engine light to come on when going up a hill?

    There are a number of possible causes. It's probably indicating a problem with the air/fuel mixture, so start by checking your fuel tank cap is tight.

    Other possible causes might be a faulty sensor, such as an O2 or MAF sensor going bad.

    Take it to a mechanic or an auto parts store and get a diagnostic check with an OBD-II scanner. Other information to give your mechanic:

    1. Does it go off when you are on a flat surface or going downhill?

    2. Were you driving at a very high altitude?

    3. Is this the first time it's happened?


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