Why Does My Check Engine Light Come On After Rain?

“Check Engine” There’s nothing fun about these two words. And there’s not much logic about them. Once the check engine light pops on the dashboard, the car computer is telling you that something is wrong with the engine.

Have you noticed the check engine light after rain? While there seem to be no connections between these two events, they are related, and the check engine light can appear after heavy rain for several reasons. So, if you are wondering why is my engine light flashing after it rains, read on to find out why it happens and how to fix it.

how to fix check engine light after rain

Why does check engine light come on after it rains?

The most common reason the check engine appears on the dashboard after heavy rain is due to cylinder misfire issues caused by moisture entering into faulty ignition coils or spark plugs. This can also happen due to water entering into defective mass air flow and O2 sensors.

Changing the defective sensors and components, such as arching plug wires, bad spark plugs, ignition coils, O2 sensors, and mass air flow sensors, will clear the light. Let’s see how this triggers the check engine light.

Cracked spark plug insulators or ignition coils

If you have old spark plugs, wires, or ignition coils, they tend to develop small cracks and cause minor arching. This arching may be insignificant to notice under normal driving conditions. But when water or moisture enters them, it will cause engine misfires, triggering the CEL on the dashboard.

If rainfall or moisture keeps dripping into a cracked plug wire, ignition coil, or spark plug insulator, it will cause a misfire that will signal the ECU. The ECU will, in turn, trigger the engine warning light. Invariably letting you know there’s an underlying problem that needs your attention.

Cracked O2 sensor

O2 sensors, also known as oxygen sensors, monitor the amount of air in the vehicle’s exhaust and forward this information to the car computer for proper adjustment. The car computer uses this data to adjust the amount of air-to-fuel ratio that enters the engine.

This sensor is, however, sealed in such a way that water will not enter it. But if there’s a crack in it, water or moisture can enter it and make it send false or no readings to the engine control unit. If that happens, the engine control unit will interpret it as an error and pop the CEL, alerting you to check the system.

Cracked MAF sensor

Much like a cracked O2 sensor, if the MAF sensor develops cracks, it will allow moisture and water to creep into it. When that occurs, it will send false or incorrect readings to the car’s computer. Invariably triggering the check engine light on the dashboard.

False Alarm

The warning light can pop up when nothing is wrong with the engine. If you diagnose the vehicle and do not find any underlying issues, you are likely dealing with a false alarm.

If you are lucky, the warning light will disappear after a few cycles when the water or moisture has dried up. Sometimes, the light will remain until you fix the root cause or wipe it off with a diagnostic scan tool. 

If you were wondering, can water make your check engine light come on? You already know; the short answer is yes. If you also have this light pop up after washing your car, you are dealing with the same issue.

What to do if your check engine light comes on after rain

If the engine warning light appears and the vehicle is running smoothly and fine, you can continue driving with it. The light will disappear after some time. It could be a false warning, but you don’t want to make a conclusion without running a diagnosis.

Whether you have a check engine light on but car runs fine or rough after rain, you should first diagnose the spark plugs, plug wires, or ignition coils, as the case may be. 99% of the time, the light appears after rain due to cracks on the plugs, wires, or ignition coils that are creating small sparks.

Here’s how to fix check engine light after rain: The simplest way to test plug wires without any tools is to start the vehicle in a dark area and watch the wires for sparks. If you notice any spark coming from the wires, there you have the culprit. But if not, keep diagnosing the vehicle.

Plug your diagnostic scan tool into your vehicle ODB port and pull out the logged error codes in the powertrain control module. If the light comes up and goes off after awhile, you should scan the vehicle when the light is still on the dashboard. Otherwise, you may not capture the culprit.

The diagnosis will often point to defective plug wires, ignition coils, spark plugs, O2 sensors, or MAF sensors. If any of these are the culprits, go ahead and replace them.

check engine light after rain toyota

When should I visit my mechanic?

You should visit your mechanic if you have tried your best and cannot address the problem. Or, if you are not the DIYer type, contact your mechanic to diagnose and address the problem. Sometimes, some minor problems are difficult to diagnose and are best left to experts.

An expert mechanic will properly diagnose all the potential causes and find the root cause of the problem. The mechanic will either diagnose the vehicle manually or with a scan tool. After that, he will fix the problem and clear the warning light.

Is blinking or steady check engine light after rain more serious?

Check engine light after rain on Mercedes, Ford, Toyota, and any other car models can come on flashing, blinking, or steady. Whichever way it comes, it means something is wrong with the engine. However, one is better than the other.

If the check engine light is blinking, you have more serious issues that need your attention. In such a case, I advise you to stop driving until you rectify the issue.

If, however, the light is steady, you have a lesser issue that still needs to be diagnosed and fixed. The causes of a steady CEL can be as minor as a loose gas cap or an improperly seated oil dipstick. You can drive with the light on for a year without major issues.

Final Words

A quick recap! The check engine light coming on after rain is due to an engine misfire caused by moisture or water entering a cracked spark plug insulator, plug wires, ignition coils, O2 sensor, or mass air flow sensor.

If the engine warning light appears on your dashboard, do not panic. Instead, follow the guidelines in this article to clear the light. Do not forget to visit your mechanic if you try but can’t track and address the issue.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

One thought on “Why Does My Check Engine Light Come On After Rain?

  1. Thanks for giving us a knowledge about the Motor vehicles mechanical problems and how to solve them, thanks a lot.

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