Getting a check engine light after replacing spark plugs can be frustrating, to say the least. However, getting to know what caused the light to show up is key to fixing any underlying problems in your car.
So, what causes the check engine light after spark plug change? Check engine light after spark plug change is due to misfire caused by spark plug installation mistakes like incorrect gapping, crisscrossed plug wires, spark wire not properly connected to plug, spark not properly tightened, and using the wrong model of spark plugs.
Read our comprehensive guide below to discover more in-depth details about why check engine light appears after spark plug replacement and how to solve the problem the right way.
Why is the check engine light on after spark plug change?
Check engine light on after spark plug is usually a sign that you didn’t do the installation process correctly.
Many mistakes can arise if you’re not careful during the spark plug change, and these will eventually trigger the check engine light after spark plug change.
The most common spark plug installation mistakes likely to offset the check engine light include:
- Using the wrong model of spark plug for your car: Using incorrect spark plugs for your car will cause misfires due to excessive heat, increased fuel consumption, quenching, and even engine failure!
- Incorrectly gapped spark plugs: If the spark plugs are not correctly gapped, they will also result in misfires. (More info on how to correctly gap spark plugs coming up later in the post).
- Spark wires not correctly connected to the plug: check that all the wires are properly secured to the plug. Also, ensure the wires are properly connected to the coils.
- Crisscrossed plug wires: You also need to ensure the wires are connected to the correct plugs. crossed spark plug wires will cause engine misfires, surging, hesitation, rough idling, and check engine light.
- Spark plug not correctly tightened: When not correctly tightened, spark plugs can result in engine problems that activate CEL. Make sure your spark plugs are finger-tightened until the gasket hits the cylinder head and then tightened an extra ½ – ⅔ turn with a wrench.
- Damaged spark plug wiring: If the wires are in bad shape during spark plug change, it’s easy to damage. We suggest replacing the wiring whenever you’re replacing the spark plugs.
All the above issues can easily cause a misfire and throw the CEL. The error codes for the underlying issues will also be thrown to help discover which cylinder is misfiring.
To be 100% sure of what’s causing the CEL, we advise you to have the error codes checked.
You can pull the code with an OBD-II reader or you can take it to a local auto parts shop to have them pull the codes for you. Most auto parts stores will give you the code readings for free.
The codes will help give you an idea of where to look or to narrow things down and make it easier to solve the underlying problem.
Will loose spark plugs cause check engine light?
Loose sparks can cause the check engine light to come on. If they’re loose, it means they’re improperly fitted and can cause various problems to your car engine.
Some of these problems include dead cylinder, pre-ignition, detonation, and engine performance issues (e.g. misfires, slow or difficult acceleration, trouble starting the engine, etc.).
If you suspect that the check engine light is on because of loose spark plugs, you should go ahead and inspect them directly.
If you can turn them with your fingers, then they’re too loose and need to be fitted properly.
To tighten the spark plugs, screw them in using your fingers. Once it feels tight, use a sparks plugs wrench to tighten them further (an extra ½ – ⅔ turn with the wrench will do).
How do you gap your spark plugs to prevent check engine light?
As we said earlier on, ungapped spark plugs will result in misfires. The gap between electrodes becomes too small or too wide that the air/fuel mixture is unable to ignite, or ignites on the wrong stroke—causing a misfire which then activates the check engine light.
You can avoid this by correctly gapping your spark plugs with the help of a gapping tool. This is how you gap your spark plugs correctly:
Step 1. Disconnect the positive (+ve) battery terminal
Step 2. Grab the spark plug and position the gapping tool between the ground and center electrodes of the spark plug.
Step 3. Now slide the gap tool between these two electrodes and increase the gap by applying light pressure.
Step 4. In case you need to narrow the gap, squeeze the two electrodes together gently. Alternatively, you can lightly tap the spark plug on towel on the table.
Step 5. Double check that the gap size is correct and you’re done! Repeat this process for all the other spark plugs you plan to install.
How long does it take for check engine light to go off after changing sparkplugs?
If the check engine light was on before changing the spark plug, then you may be wondering how long it will take to go off after the replacement.
The truth is, the check engine light will not go off immediately after you replace faulty spark plugs. This is because the light needs more time to reset.
During this time, your car computer checks all the sensors to ensure everything is running fine.
You can, therefore, expect the CEL to go off after you drive around for a while—this is usually 50 to 100 miles in most cars.
In Some vehicles, all you have to do is take your car through a given number of drive cycles (a drive cycle is where you turn the car on and off) and the light goes off after that.
If after driving for a while your check engine doesn’t reset, it means there’s an issue you’re not aware of and you should consider checking whether you did the replacement for spark plugs correctly.
Should you reset the computer after changing spark plugs?
You can reset the computer after changing spark plugs, but this is optional. You can do the rest using various proven methods.
One such method involves using the OBD II scanner to erase the codes and clear the check engine light.
Disconnecting the battery is another method you can employ to clear the codes and reset the computer. This involved disconnecting the battery negative terminal for at least 15 minutes and then hooking it back.
If the check engine light comes back on after a while after resetting the computer, it means your car has an unresolved issue that requires your attention.
don’t ignore this light. Go to an auto parts shop to have your car codes read to uncover what issue your car is warning you about.If you’re experiencing a check engine light after changing your spark plugs, there could be several reasons behind it. One possible cause is an issue with the ignition system, which can trigger the check engine light to come on after the spark plugs have been changed. However, if you have already checked the ignition system and the light is still on, you may want to consider other causes, such as issues with the battery or oil. Our articles on troubleshooting check engine light issues can provide valuable insights into the problem. For example, if you’re experiencing a check engine light after a dead battery, our article on after dead battery may be helpful. This article covers common causes and solutions for check engine light issues that arise after a dead battery. Similarly, if you’re experiencing a check engine light after changing your oil, you may want to read our article on after oil change. This article discusses potential causes and solutions for check engine light issues that arise after changing your oil. Take a look at these articles for expert advice on diagnosing and fixing check engine light issues.
1. Should spark plugs change cause an engine light?
No! Spark plug change should NOT cause the engine light to come on, provided you did the spark change properly. If you get the CEL, it means you messed up somewhere during spark plug change or it’s just a pure coincidence. Have the error codes read to give you an idea of what problem your car is having.
2. What should I do after changing spark plugs?
After changing spark plugs, start the engine to ensure the sparks are as they should be. If the engine starts smoothly and the check engine light doesn’t illuminate, you did the job correctly. In case the engine fails to start, you should look for a mechanic to diagnose your vehicle for underlying problems.
3. Why do I still have a misfire after a spark plug change?
Misfires after spark plug change mean the spark plug isn’t firing properly. This could be a result of errors during the installation process such as incorrectly connected wire, mismatched spark plugs, damaged spark plug wiring, etc. You should double-check your installation and correct any errors to repair the misfire and get rid of the blinking check engine light.
After you successfully change spark plugs, it’s common for the check engine light to appear in most cases. When this happens, don’t panic. It simply means you may have screwed up when doing the installation and it’s resulting in misfires. Misfires are notorious for triggering the check engine light.
Just go back under the hood and check that you use the correct models of spark plugs, the sparks are correctly gapped, and ensure the wires are properly connected and none of them is crisscrossing the other. You also want to ensure your spark is the right tightness; not too loose and not too tight.