Rick's Free Auto Repair Advice

What does a check engine light mean?

A check engine light means the computer has found a fault in a major system

All modern vehicles have at least one computer to run the engine and transmission. Those computers take in data from sensors like the intake air temperature sensor, oxygen sensor(s), engine coolant temperature sensor, manifold absolute pressure sensor, and the mass airflow sensor. If the data is outside of normal specifications, the computer will set an internal trouble code and turn on the check engine light. Here’s how to find out what a check engine light means on your car.

Most auto parts store will read the trouble code for free

But keep in mind that they’re in business to sell parts. So they’ll recommend replacing whatever part is listed in the trouble code. If you follow their advice, you’ll replace a lot of parts and still have the code. But getting the trouble code is not a diagnosis. The part mentioned in the code may be telling the truth and the root cause for the bad data is due to some other issue. A lot of DIYers have wasted a lot of money replacing whatever part was listed in the code without doing any diagnostic work. If you don’t diagnose the problem, then you’re just throwing parts at it.

How much does it cost to get a professional diagnosis?

Most shops charge a minimum one hour diagnostic fee to determine the cause of the check engine light. Many DIYers think that a diagnostic is as simple as polling the computer to see what codes are stored. That’s wrong. Only a hack technician would make a diagnosis with just the code.

Can you still drive with a check engine light on?

In most cases, yes. If the check engine light isn’t flashing and your vehicle is driving normally, you can continue driving until you have an opportunity to get it into a shop to be diagnosed.

However, if the check engine light is flashing, that’s an indication of a serious misfire that could cause expensive damage to your vehicle’s catalytic converter. Converter replacement can cost thousands. So if your check engine light is flashing and you can’t get it to stop flashing by backing off on the accelerator pedal, pull over can get it towed to a shop. A tow will cost a lot less than a new catalytic converter.

What are the most common causes of a check engine light coming on?

Misfires, caused by ignition, fuel or mechanical problems
Emissions issues caused by leak in the evaporative emissions system or exhaust system
Air/fuel related problems caused by air/vacuum leaks or faulty oxygen sensors


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Posted on by Rick Muscoplat

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