Cracking the Check Engine Light Code: Understanding Its Meaning
The check engine light is turned on whenever your car’s internal computer discovers a problem with the car’s engine or transmission. Unfortunately, that means there could be a long list of reasons, ranging from a loose gas cap to a faulty catalytic converter.
If it just turned on, it’s unlikely that you’ll run into problems instantly. Some modern cars may have a solid or flashing indicator with the latter meaning that you should pull over right away. In any case, it should be considered as warning lights for you to get your car to a repair service as soon as possible.
What is the check engine light?
The check engine light is often displayed on the dashboard in one of two forms—either a car’s engine icon and the words “check” or just as two words “check engine”.
Due to the many possible reasons and the rather uninformative nature of the light itself, it’s one of the most frustrating indicators. Additionally, in some countries, just having the light on will mean that your car will be unable to pass technical tests required for registration or renewal.
Common reasons the check engine lights illuminate for
There are two main ways you can narrow down the reasons for the check engine light - by using an OBD2 diagnostics tool or by going through the list of the most likely occurrences. While the latter does work, the former is much more reliable and accurate.
1. Faulty oxygen (lambda) sensor
The oxygen sensor measures the emissions from the fuel mixture, which is then transmitted to the engine control unit. If the mixture is improper, the control unit changes the quantity of fuel.
A faulty oxygen sensor means that the control unit cannot properly change the fuel mixture, which can cause many issues such as engine misfires, rough idling, or bad fuel economy. As such, a malfunctioning sensor can be one of the more common reasons for the check engine lights to pop up.
2. Ignition coil failure
Ignition coils send the voltage to spark plugs. Similarly to the oxygen sensor issues, a malfunctioning ignition coil may send an improper voltage to spark plugs, which may cause an engine misfire, rough idling, and other changes into how your car runs.
Since ignition coils directly affect the engine, the associated dashboard light will illuminate if one of them is failing. Replacing them should fix the issue and resolve most engine issues.
3. Spark plug issues
A spark plug takes the voltage from ignition coils and produces the spark that ignites fuel. If they are worn out, an adequate spark may not be produced, which may fail to ignite the mixture.
Almost identically to ignition coils, failing spark plugs will cause rough idling and engine misfires. They’ll also cause the check engine light to illuminate. Additionally, it may also cause fuel to leak through the exhaust pipe due to it not being ignited properly.
4. Failing fuel injector
As the name suggests, fuel injectors push fuel into the combustion chamber. Other parts, such as the ignition coil, take over the process to complete the combustion cycle.
Faulty fuel injectors will either push too little or too much fuel into the combustion chamber, causing the engine to run too lean or too rich. Both cases may affect engine speed and work efficiency, cause misfires or rough idling.
If the check engine light is on and there’s unusual sounds (such as hissing) coming from the engine compartment, a faulty fuel injector could be the culprit.
5. Loose gas cap
One of the easiest issues to fix is a loose gas cap. The fuel pump requires a complete vacuum to operate correctly, however, a loose gas cap will cause air to disrupt it. In turn, the mixture may receive more oxygen, which may cause misfires or rough idling.
In general, any malfunctioning oxygen management part (such as airflow sensors) will cause the check engine dashboard warning lights to illuminate.
Luckily, often, all it takes to fix a loose gas cap is to simply tighten it up. If it’s broken, getting a replacement is usually extremely cheap, so you could consider yourself lucky if a loose gas cap is the reason for a check engine light.
6. Catalytic converter issues
If a loose gas cap was the easiest issue, converter issues are one of the worst possible reasons for the engine warning lights to illuminate. They are used to filter and clean emissions for which precious metals are utilized.
Due to the precious metals used, catalytic converters are one of the most expensive parts to replace. Leave them as the last possible reason for the check engine lights.
Understanding check engine light codes
While the true check engine light meaning is usually almost impossible to deduce from the dashboard, there’s an easy fix to it—OBD2 diagnostic scanners. These devices connect to the car’s onboard diagnostics system to retrieve information from the vehicle’s computer.
If the check engine light has illuminated, then a diagnostic code can be retrieved with an OBD2 scanner. These will be more descriptive than the check engine light as they will point to an exact issue.
Some OBD2 diagnostic tools are also able to retrieve manufacturer-specific codes, which are even more informative and precise. As such, these tools are lifesavers if you want to diagnose check engine light issues.
Here are some of the most common error codes you’ll find if the check engine light is on:
P0130: Oxygen sensor malfunction.
P0131: Oxygen sensor low voltage.
P0171: (Fuel) system is too lean.
P0172: (Fuel) system is too rich.
P0173: Fuel trim malfunction (means the ratio of fuel-to-air is off).
P0200 to P0201: Fuel injector circuit malfunction. P0200 indicates a general malfunction, P0201 indicates malfunction in cylinder 1.
P0300 to P0303: Indicates engine misfires. P0300 indicates misfire of multiple cylinders, P0301 to P0303 is related to cylinder 1 to 3.
P0351 or P0352: Fault in ignition coils A (P0351) or B (P0352). Either can also indicate a general circuit malfunction.
P0420: Low catalytic converter efficiency.
P0430: General catalyst system malfunction.
There are always more possibilities and codes, but using an OBD2 scanner can help you understand the source of the issue and the severity of it. In these cases, the scanner removes all of the guesswork out of the check engine light issue.
Preventing check engine light issues
If you use any car long enough, check engine light issues are almost inevitable. But there’s a lot you can do to reduce the likelihood of having the dreaded check engine light pop up.
Many of the issues we’ve listed above are general wear-and-tear. While driving behavior may have an effect, regular servicing and taking care of the car will go a much longer way.
For example, spark plugs should be replaced regularly, according to the manufacturer’s recommendations. Some of them may last longer and continue working as intended, however, to avoid any potential issues, the manufacturer’s guidelines should be followed as closely as possible.
Other regular maintenance recommendations such as oil changes may help in preserving parts of your car that would otherwise force the check engine light to pop up.
Additionally, if you are required to replace some parts of your car, the aftermarket shouldn’t always be the first option. Getting parts will reduce the likelihood of issues, which could otherwise cause the check engine light to illuminate. Car tuning could also cause check engine light issues.
Finally, having an OBD2 scanner at the ready is always a nice touch. Many modern and more advanced OBD2 scanners will give you access to various data points (and even live data) collected by the on-board system.
It’ll be a lot easier to perform preventative maintenance and to take care of your car if you have all the information you need within hand’s reach at all times.