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What does the check engine light mean?

By David Bonnici, 17 Aug 2018 Car Advice

What does the check engine light mean?

This is one of the misunderstood dashboard warning lights. What does it mean and what should you do when it comes on?

For the majority of drivers who aren’t very mechanically minded, the amber glow of the check engine dashboard light can be quite alarming.

The good news is, in many cases, its illumination isn’t necessarily a sign that your engine is about to seize and send you into a world of financial pain.

The check engine light will either blink or remain constant, depending on the issue.

A steady light means the problem isn’t serious and, providing there are no other warning lights, the engine sounds and feels ok and the water temperature is normal, you should be right to keep driving. Just be sure to get it checked out as soon as possible.

Quite often the check engine light will come on because the car thinks fuel isn’t burning properly. This could be caused by anything from a faulty oxygen sensor that measures unburnt oxygen in the car’s exhaust, spark plug issues, and even not tightening your fuel cap properly.

Either way, while your car is still driveable, you should have the vehicle checked by a mechanic as soon as possible.

A blinking light usually indicates something more sinister, such as an unburned fuel being dumped into the exhaust system which can damage the catalytic converter. If the light flashes, drive your car home carefully, reducing power where possible, and get it checked out immediately.

The first thing a mechanic will do to find out why the check engine light is on is use an ODB2 diagnostic scanner, which plugs into a port under the dashboard of any car built since 1996. This tells mechanics about many aspects of the car’s performance including faults, which all have their own code. The code helps quickly rectify the problem without having to spend a lot of time troubleshooting. The scanners also turn the check engine light off once the issue has been fixed.

ODB2 scanners are actually easy to use and cheap to buy – as low as $20 for ones that let you read the codes on your phone via Bluetooth. Alternatively you can have this done at an auto accessories store for around $10 to $20. The good thing DIY diagnosis is you can have a good idea of what’s wrong with the car and know what action to take so no mechanic tries charging you $200 just to tighten the fuel cap.

If the check engine light comes on

  • Look, listen and even try sniffing out any potential serious problems
  • Check your dashboard gauges  and lights for indications of low oil pressure or overheating. These conditions mean you should pull over and shut off the engine as soon as you can find a safe place to do so.  
  • Try tightening the fuel cap. If this works it might take a few days for the check engine light to turn off.
  • Try disconnecting the car battery for about 10 minutes. This resets the car’s sensors and will stop the check engine light coming back on if the problem was temporary.
  • If the check engine light is blinking, reduce the strain on your engine by not over-revving or towing anything. Any serious problems will normally be accompanied by other symptoms.
  • Have the code read with your own scanner or at an auto-accessories store and if necessary get problem fixed. A good mechanic will test and fix the problem and charge accordingly, but there will always be a few who will take advantage of a driver’s ignorance so it’s always good to show you know what you’re talking about.