Check Engine light after Transmission Fluid Change – Causes and Fixes

Did you see the check engine light after transmission fluid change? If yes, take a moment to read this article to the end. You’ll learn the possible causes and the solutions to each of them.

Generally, transmission solenoid is the common reason the check engine light illuminates after changing the transmission fluid. It could be you unplugged or broke the solenoid. However, there are other possible causes. The best solution is to pull out the logged error codes to determine and fix the exact cause.

In this article, I’ll explain all the possible reasons why the check engine light appears on the dashboard and the best solutions for it.

why is my check engine light on after transmission fluid change

Check engine light after transmission fluid change – causes and Solutions

A few factors can lead to problems after transmission fluid change. If the check engine light appears after changing the transmission fluid, it’s possible you have a compromised transmission solenoid. It could also mean the transmission fluid is overfilled, low, dirty, or you used the wrong fluid.

Read Also: Why Check Engine Light Came On After Oil Change

Compromised transmission solenoid

Under normal conditions, changing the transmission fluid should not cause the check engine light to come on. But if it happens, you should check the transmission solenoid. You may have broken or unplugged it while changing the transmission fluid. The best solution is to replug or replace the compromised solenoid.

The transmission solenoid is responsible for regulating how the transmission fluid flows throughout the transmission. It directs how the fluid should flow within the system. If the solenoid is unplugged or broken, there will be issues with how the fluid gets distributed. The powertrain control module (PCM) or the transmission control module (TCM) will trigger the check engine light on the dashboard.

To resolve the problem, slide under the vehicle and locate the transmission solenoid. Check if it is broken or unplugged and re-plug or replace it as needed.

Overfilled transmission fluid

If your transmission jerks after fluid change or the check engine light appears on the dashboard, you may have overfilled the transmission.

Too much transmission fluid will not directly cause the check engine light to come on but it will cause problems that will trigger the engine light.

Overfilling the transmission fluid will not allow the transmission to breathe properly. It will cause the fluid to foam and lose its lubricating properties. If the fluid is no longer lubricating the transmission as it should, the TCM or the PCM will trigger the check engine light to notify you of the underlying problem.

Aside from that, overfilled transmission fluid will cause leaks. Since the fluid is too much, it’ll be forced to leak from areas like the drive shaft seals and the axillary gear joints.

The best solution to this problem is to reduce the fluid to the recommended level. That will stop the leaks and prevent the fluids from foaming.

Low fluid level

The primary function of the transmission fluid is to make shifting gears less strenuous by cooling and lubricating moving internal parts and bearings. It also helps with the valve body and torque converter operations.

If you do not fill the fluid to the appropriate level, it’ll not carry out its cooling and lubricating job very well. This can lead to transmission slippage and transmission overheating.

Wait a second. Does the check engine light come on for low transmission fluid? Yes, the check engine light will come on when you have low fluid. Not because the fluid is low, but because of the problems caused by the low fluid.

In this case, the best solution is to top up the transmission fluid to the recommended level.

Bad or dirty fluid

Changing the transmission fluid with a dirty or bad fluid is as bad as not changing it in the first place. Sometimes, mechanics use a transmission fluid with the one they removed from another vehicle. This may sound odd, but believe me, some mechanics do it.

If you own a luxury car, you won’t be a victim of such an act. This is because the mechanics usually keep the oil they changed from luxury cars and use it on older vehicles. While this malicious act will give them extra cash, it’ll end up causing damage to the cars they use it on.

The dirty fluid will cause the check engine light to come on. Also, you likely have dirty transmission fluid if your automatic transmission won’t go into gear after fluid change.

The only way to fix this issue is to change the dirty fluid with a new one. Have your mechanic drain the bad fluid and pour in new fluid.

Wrong transmission fluid

Car manufacturers produce their cars with different technologies. Hence, they have recommended products that will meet their car specifications.

The transmission is critical and one of the most expensive car parts. The manufacturers recommend the best oil that will suit their transmission.

Putting the wrong fluid into the transmission will trigger the check engine light. However, the car computer doesn’t know when you use the recommended fluid. It only sets the warning engine light when the wrong fluid starts creating issues in the system.

The best solution to this problem is flushing transmission after putting in wrong fluid. If you discover you changed the transmission with the wrong fluid, flush the transmission and pour in the recommended fluid.

Read Also: Check Engine Light Came On After Tire Change

Final Words

Under perfect conditions, transmission fluid change should not trigger the check engine light. However, if it does, you likely have overfilled transmission fluid, low fluid, dirty fluid, wrong fluid, or compromised transmission solenoid. It’s best to check these, one after the other, to determine and resolve the cause.

Follow this guideline, and you will track and address the check engine light issues after transmission fluid change.



While growing up, I knew I had a thing for car repairs though my parents never wanted me to learn mechanics. I always visit a mechanic garage in my small neighborhood after school. As I grew older, at age 16, I got addicted to anything automotive. My parents had to enroll me in that mechanic garage since giving up was never an option for me. As a dedicated mechanic who got into the industry from an early age, I'm graced with an addiction to diagnosing and rectifying automotive problems with ease.

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