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What does it mean if the Check Engine Light is On?

Quick Answer: You will need a Scan Tool to see what the fault is and clear this fault. Click here to view the Scan Tool.

It may be a minor or major engine fault, but we should never (ever) ignore it. In today’s article, we talk all about the check engine light (CEL)- what does it mean if it’s on, its causes, and how to reset it.

We all had that moment of panic when we saw our CEL come on while driving, right? To refresh your memory, it is that yellow, red, or amber light that illuminates or blinks on your dashboard similar to the image below:

Check Engine Light Is On
Check Engine symbol
Check Engine Light symbol

And it gives limited information all it is telling you is that there is a problem and you need to get it checked out. And sometimes, it will put your vehicle into limp mode which means your car is limited in the speed and Revs it can do. 

What does it mean if the check engine light is on?

From the name itself, the check engine light (or more technically known as the malfunction indicator lamp or the international check engine symbol), warns drivers of errors or defects on your vehicle – minor or major. 

From loose gas caps that only require your action to damaged catalytic converters that need major repairs, the CEL turns on as designed. And it is the way for the vehicle to tell you to “get up and do something about the problem now”!

What caused the check engine light to turn on?

When your vehicle’s engine computer signals you of an error through the CEL, it may be because of one (or more) of these car components;

1. Oxygen sensor/s 

Oxygen Sensor
O2 sensor

This sensor (or sensors) measures the amount of unburned oxygen in your exhaust system. And the data it sends out makes it easier for the vehicle’s computer to determine the right mix of air and fuel in the cylinders.

Although your car can still run with a faulty sensor, not replacing this for a long time can cause less fuel economy and damage to your spark plugs and catalytic converter. Also, some newer vehicles may have multiple oxygen sensors, so make sure you replace the correct one. 

2. Fuel cap

Loose Fuel Cap
Loose fuel cap

Even a loose fuel cap triggers the car’s computer to turn on the check engine light If not screwed on properly, the entire gas tank recirculation system (or EVAP emission control) becomes compromised. 

Loss of fuel through evaporation and the constant flashing of the CEL should be enough to force you to (properly) seal the fuel cap. 

3. Catalytic converter

Catalytic Converter
Catalytic converter

The catalytic converter converts harmful carbon monoxide produced by the vehicle during the combustion process into carbon dioxide before being emitted into the atmosphere. This is a simple yet essential device, especially in passing emissions tests. 

Regular maintenance checks will do the trick to prolong the life of your catalytic converter. Doing this will also ensure good engine performance and fuel economy, while saving hundreds of dollars on labour costs and replacement parts. This is the one part you always need to inspect once the check engine light comes on. 

4. Ignition system

Spark Plugs and wires
Spark plugs and wires
Ignition Coils
Ignition coils

Do you experience engine misfires, reduced engine performance, a rough idle, or an uneven acceleration? And do you see the check engine light flashing? Then you might look at a defective spark plug, failing ignition coils, or damaged spark plug wires.

There is no other recourse for fouled spark plugs and wires than to replace them. For coils, though, you may need to swap them with other coils (most cars have one coil per cylinder) to find out where the fault is happening. 

5. Mass airflow sensor

Mass Airflow Sensor
Mass airflow sensor

This regulates the amount of air that enters the engine cylinders. Too little or too much air will cause damage to the engine and can also affect fuel economy. 

The mass airflow sensor is sensitive to any contaminant (i.e. oil, dirt, water droplets) and will trigger the CEL if a significant amount builds up around it. 

6. Vacuum system

Vacuum System Wire
Car vacuum system wire

The vacuum system in an engine performs a host of functions such as supporting the brake booster and helping diffuse harmful emissions from the engine. However, when leaks on vacuum hoses happen, the RPM when your car is in idle will either surge or not be at its normal level. 

Replacing the damaged vacuum hose is the best way to fix this. However, finding which hose can be cumbersome and confusing, especially if you’re not well-versed in doing this task. 

7. Exhaust gas recirculation (EGR) valve

EGR Valve
EGR valve

The EGR valve helps burn fuel by redirecting exhaust gases back to the combustion chamber. It also lowers the amount of nitrogen oxide emitted by the engine.

This is also one of the easier engine parts to uninstall, clean, and install again. So, if the check engine light flashes, and you found the EGR to cause the fault, fix it immediately. 

How to check what the problem is?

The CEL may blink, flicker, or stay on for a certain period. Be more concerned with the steady blinking, though. This usually spells serious engine trouble, and you may need to visit your mechanic soon. 

Nevertheless, as a general protocol to follow, monitor the performance of the vehicle and mind the condition you are in when the check engine light comes on (i.e. off-road driving, city driving, ambient temperature). Then, slow down and pull over to do a quick check on critical car parts mentioned above if you can. 

Check Engine Light Is On
Car Engine

The car’s computer stores the data of errors that cause the CEL to turn on. We call these diagnostic trouble codes (DTC). These codes are standardised for car models manufactured in the USA from 1996 onwards under the OBD2 protocol. The rest of the world soon followed, and now, most vehicles here in Australia are OBD2 compliant from 2007. 

To read these codes and determine what error the CEL is pointing to, you will need an OBD2 scan tool (If you still have an OBD1 car, check this out). Plug in this tool onto your OBD2 port and the DTCs will appear on your handheld device, laptop, or mobile phone. You will then need to read through these codes to pinpoint what component to fix. 

How to clear the check engine light?

The same OBD2 scan tool that helped you diagnose the problem in your engine, can also clear and turn off the check engine light. Again, plug in your diagnostic tool and select the option to reset the check engine light.

Check Engine Light Is On
Check Engine Light
CEL Reset
Check engine light reset

Our Final Word

Now we’ve discussed the check engine light, once it comes on, you now have no reason to panic. Right?

Regardless, follow our guide when the CEL indeed to observe the engine performance, and then to slow down and pull over. Monitor the vehicle and if you have your scan tool with you, then perform a diagnostic scan there. 

If you can’t find the defect, and you don’t have a diagnostic tool with you, it would be wise to seek professional help as soon as possible. 

Check Engine Light Is On
Car dashboard
Check Engine Light reset

How long can you drive with the engine light on? You never know. If the fault is minor, then it may be fine. However, a minor error can develop into more serious engine issues that may cause catastrophic damage to your vehicle.

Our actual final word? Don’t wait until the check engine light turns on in the middle of your drive. Nothing saves more money and time than a routine preventive maintenance to keep your vehicle healthy and happy!

Do you have more questions on check engine light or your vehicle? Talk to us! We look forward to that conversation.

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