How to Fix Your Check Engine Light After Changing Spark Plugs [3 Simple Fixes!]

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check engine light after changing spark plugs

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Changing spark plugs is among the easy engine-related repairs one can do on their vehicle without needing a professional. However, there are potential dangers during the replacement, some of which can cause the check engine light to come on.

The check engine light can come on after a spark plug change if any of the new spark plugs are loose. The light may also come on if the spark plug wires are defective or loose. However, the light may not be unrelated, which you must diagnose further to know.

Read on to learn why you may have the check engine light on after changing spark plugs and the solutions.

check engine light after changing spark plugs

Why Check Engine Light Comes On After Changing Spark Plugs [3 Possible Causes & Solutions]

The check engine light can come on for hundreds of reasons, most of which require diagnostics to tell. However, if the light came on after you repaired or replaced a part, the two events may be related. In this instance, if the check engine light came on after changing the spark plug, it may be responsible.

I usually find changing spark plugs easy, and like most people, I can do it in under one hour. However, you may need basic knowledge of various things, like how long to let the engine cool before changing the spark plugs.

Following are some of the reasons the check engine light may come on after changing the spark plugs.

1. The new Spark Plug Is Loose

One of the reasons the check engine light may come on is if the new spark plug is loose. When loose, the engine can ignite early, causing pre-ignition or misfire. When the system detects this problem, it can trigger the check engine light.

Overtightening the spark plug can also crack the insulator or damage the head bolts. The damage can prevent the spark plugs from installing properly the next time you change them.

Solutions

A loose spark plug needs to be reinstalled and tightened correctly. Usually, you can tighten the spark plug with your fingers and then do a half-turn with the spark plug wrench.

I usually consult the user manual on any part that needs tightening to know their torque specifications. This knowledge can save you from the troubles that come with over-tightening a part.

However, if you’re uncomfortable with this repair you can get a mechanic to replace and tighten them correctly. You can pay anywhere between $15 and $100 for the replacement, depending on the car type and the repair store.

2. Faulty Spark Plug Wire

Another reason the check engine light may come on is if the spark plug wires got damaged during the replacement. The wire may have become broken, causing it to interfere with the current flow and resulting in a misfire.

Solutions

Replace the faulty spark plug wires if they are causing the light to come on. The symptoms of a bad spark plug wire resemble that of a worn-out spark plug, including the vehicle jerking and stumbling. This fact is why I prefer to change both spark plugs and their wires when I detect a misfire problem.

After purchasing the new spark plug wires, follow the steps below to replace them. Ensure the engine is cool.

  • Step 1. Rotate and pull to remove the spark plug wires, starting with the longest ones.
  • Step 2. Compare the sizes of all the wires not to confuse them and their position. Also, note the wire boot color or shape to know which ends go into the spark plug and cap.
  • Step 3. Install new spark plug wires routing them the same way the previous ones.
  • Step 4. Start the vehicle and test for misfires and other problems you detected before the replacement.

You can also hire a professional to change the spark plug wire for you and minimize the chances of other faults. The cost of replacing spark plug wires averages at $130, but you may need to pay more than $200 for high-end vehicles.

3. Not Yet Completed the Cycles

Usually, the check engine light remains on for some time after successfully replacing the faulty part before automatically turning itself off. In this situation, if the light was on before you changed the spark plugs, you may not have completed the cycles yet.

Cycles are instances where you turn on the vehicle, run it for some time, then turn it off. The light automatically comes off after ten cycles or more, but usually not more than 20. Some vehicles may also reset after driving more than 50 miles.

Diagnosing the Check Engine Light That Came on After Changing Spark Plugs

The spark plug may not be the reason the check engine light is on. Various people have also reported the check engine light came on after a tire change. However, the vehicle needs further diagnosis to tell the problem.

While you can get a professional to diagnose the car, you can also do it using a scan tool. Also, some auto parts stores, like AutoZone, do the scan for free through their free Fix Finder service.

After securing your Onboard diagnostic II scan tool, follow the steps below to check why the engine light is on.

  • Step 1. Locate the port. It’s usually just on the left on the driver’s side
  • Step 2. Connect the scan tool
  • Step 3. Consult the scan tool’s instructions to check whether you need to turn the vehicle on
  • Step 4. Scan
  • Step 5. Read codes and fix the problem

People Also Ask

Following are the frequently asked questions on this topic, along with their answers.

Can You Turn the Check Engine Light Off After Changing Spark Plugs?

Some scan tools allow you to turn off the check engine light after a scan. Using the tool, you can disable the check engine light. However, resetting the light usually involves clearing all the DTCs which are needed in diagnosing and fixing the actual issue.

Will Disconnecting the Vehicle’s Battery Turn Off the Check Engine Light After Changing the Spark Plug?

Disconnecting the car battery usually resets the check engine light. The Battery should be off for about three minutes to ensure the system is drained. However, if the spark plugs are causing the problems the light will come back on.

Concluding Words

Spark plugs are one of the common causes for the check engine light to come on. Any of the newly installed spark plugs may be loose if the check engine light comes on after you replace them. However, you may have damaged the spark plug wires and must replace them.

The best idea is to always diagnose the vehicle using a scan tool or take it to service stations for a checkup. Once your scanner shows the reason for the light, take the vehicle for repair.

Resources

  1. https://www.uti.edu/blog/automotive/spark-plugs
  2. https://www.wikihow.com/Change-Spark-Plugs-in-a-Car

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