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Toyota Prius Check Engine Light Diagnosis (Troubleshoot Guide)

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Diagnose and clear your check engine light!

We’ve scanned over 14,945 Toyota Priuses with the FIXD OBD2 scanner and app. These are the 5 most common reasons for a check engine light in your Toyota Prius.

5 Most Common Reasons for a Toyota Prius Check Engine Light to Come On

See how to easily find out why your check engine light is on and turn it off!

Code Severity  Simplified Description
P0A80 SEVERE – Stop driving immediately There is a problem with your hybrid battery system, which is the big battery that drives the car. The red triangle warning light may turn on at the same time if this is the case.
P0420 MODERATE – Extended driving with this code can cause internal engine damage Your catalytic converter isn’t functioning efficiently. This could increase the output of harmful pollutants.
P1121 LOW – Continued driving for a short period of time is okay There is a problem with your three-way coolant flow control valve or its associated sensors. This system supplies heat to the interior, and is not a critical cooling system like the radiator.
P0300 SEVERE – Stop driving immediately Two or more cylinders are experiencing misfires, which could cause damage to your engine or emissions system.
P0301 SEVERE – Stop driving immediately Cylinder number one is experiencing misfires, which could cause damage to your engine or emissions system.


Diagnose Your Toyota Prius Check Engine Light in Seconds

Read and clear over 10,000 check engine lights from your phone using the FIXD Sensor and free app!


Other Common Toyota Prius Issues

  • Center multifunction display failure
  • Heat not working

Why has my center multifunction display stopped working?

The Prius center multifunction display is a sophisticated electronic device. One of the most common problems the Prius has is this display going dark and not working. This is usually because one of the solder joints in the inner circuitry has gone bad. You can replace this display, but you may also be able to have your existing display repaired. Once the faulty solder joints are fixed, the display will work normally again.

Why isn’t my heat working?

If this happens and your check engine light turns on, triggering a P1121 code, most likely your Prius’s three-way coolant control valve has failed. Because it’s a hybrid car, the Prius is designed to provide heat even when the gas engine isn’t running. It does this by storing coolant heated by the engine while it’s running in a special storage tank. The hot coolant then circulates through your heater core, providing heat while the car is running on purely electric power. The valve that controls the flow of coolant between the engine, heater core, and hot coolant storage tank, can get stuck, or the electronics controlling it can fail. The fix for this problem, and this trouble code, is to replace this valve.

Check Your Gas Cap

One of the most common reasons for a Prius check engine light is also the easiest problem to fix: a loose gas cap. This happens because the engine detects a leak in the evaporative emissions system, which exists when the gas cap isn’t tightened until it clicks. It’s easy, and it’s free! Learn everything there is to know about Evaporative Emission Control (EVAP) System, including the various components and how they work, by reading this article.

What Should I Do If the Check Engine Light Is On in My Toyota Prius?

There are many issues that can cause the Toyota Prius check engine light to turn on, from a loose gas cap to major engine issues. If this light turns on, don’t panic. Check out our guide on what to do when your check engine light comes on. Following this guide can help you avoid driving with a serious problem and causing more damage to your engine. 

If you’d like some more information on diagnosing a check engine light yourself, you can also check out our article on the most common reasons for a check engine light.

For those of you who prefer a mechanic, you can find a trusted repair shop for inspection easily with RepairPal.

> Find a RepairPal Certified Shop Near You

What the Check Engine Light Means

Your Prius engine light is part of the onboard diagnostics system (OBD2). Read our full OBD2 scanner guide to learn all the OBD2 basics, including how to use it and understand the codes. All gas-powered cars and trucks made since 1996, plus diesel cars and trucks since 2008, have a diagnostic system to manage the engine and monitor system performance. This system alerts the driver and service technicians to any engine problems by turning on the Check Engine Light on your dashboard. Special tools known as code readers, or OBD scanners, can access diagnostic information from this system to find out what’s wrong with your car and how serious the problem really is.



Instantly Diagnose Your Toyota Prius Check Engine Light

Read and clear 7000+ check engine light codes with the FIXD Sensor and free app.



How to Read Your Toyota Prius’s Check Engine Light

There are a few ways you can read the diagnostic trouble code stored in your car’s computer.

Browse our detailed guides here to learn more about OBD2 codes.

1) Go to your local mechanic. A shop can plug in their professional scan tool to read the code and identify the cause of the problem. They will usually charge a diagnostic fee for this service. It also won’t help you if you’re broken down on the side of the road. Additionally, you may not have a relationship with a shop that you trust to diagnose the problem accurately, rather than try to profit from repairs. 

2) Go to a nearby auto parts store. Most parts stores have an OBD2 scanner they can plug into your car and read the code and technical description for free. The person providing this service is likely not a mechanic, though, and may not be able to provide any more information than what the scanner tells them. It’s also possible that they may try to sell you products you don’t need in order to “fix” the problem.

3) Read your own check engine light codes with or without a scanner. Checking codes manually can be done but, it’s tedious. Borrowing a scanner or buying one makes the process easier. There are many OBD2 scanners you can buy that will read codes and provide other engine information anytime you want. Read about our top picks for OBD scanners here. FIXD is able to translate any Toyota check engine light into plain English directly on your smartphone. 

How the FIXD Check Engine Scanner Works

The FIXD car scanner plugs into your car’s OBD2 port. This is a trapezoid shaped plug located under the driver’s side of the dashboard. Read more about how to find your OBD2 port on your particular car. You can read our detailed guide with illustrations on how to locate your OBD2 port.

most common locations for OBD2 port in carMost common locations to find your car’s OBD2 port

The FIXD Sensor and free mobile app explain in plain English what problem codes your car has recorded. You will get a detailed description of the problem so that you can make informed decisions about repairs.

Understand Your CEL

FIXD instantly translates over 7,000 error codes into simple terms right on your phone.

FIXD Scan History

See How Serious Your CEL Is

Find out if your problem is serious or not, and whether it’s safe to keep on driving.


Get Maintenance Alerts

FIXD can automatically alert you when your Toyota Prius is due for an oil change and other routine maintenance, based on your specific model and its mileage.

FIXD Maintenance Log

Monitor the Health of Your Toyota Prius

FIXD will immediately send a notification to your phone if your check engine light turns on. You can also monitor data in real time, such as oxygen sensor voltage, fuel trims, vehicle speed, and more. Read this article to learn how the FIXD scanner and app’s live data function allows you to literally talk to your car when diagnosing most check engine light problems.

FIXD Live Gauges app display

Does FIXD Work with Your Toyota Prius?

FIXD is compatible with 1996 or newer gas-powered Toyota models, as well as 2008 and newer diesel cars and trucks. Use the Compatibility Checker for additional info.

That depends on what issue caused the light to turn on in the first place. You will need to use an OBD2 scan tool like the FIXD Sensor to learn the exact nature of the problem, how severe it is, and whether or not it’s safe to keep driving.

Generally speaking, if the indicator is a steady yellow light, it should be okay to keep driving. This could be something like an emissions issue that doesn’t affect drivability. Your car will keep running just fine, but it’s still best to get this diagnosed and repaired sometime soon, especially if you live in a state that performs vehicle inspections.

If the light is blinking, you should stop as soon as it’s safe to do so. This indicates a serious problem, such as a misfire, that is actively occurring. It’s also good to check for low oil or overheating. If your check engine light is red, you should stop driving immediately.

If your Prius experiences driveability issues, such as reduced power or misfires, slow down and take it easy on the engine to avoid making the problem worse.

How Can I Reset the Check Engine Light in My Toyota Prius?

If you think you have resolved the problem, you may want to clear the codes that triggered your Toyota Prius check engine light. If you reset the light, drive, and it doesn’t turn back on, your problem is fixed. Our detailed guide shows you how to quickly reset the check engine light without disconnecting the battery.

The easiest way to reset the check engine light on your Toyota Prius is with FIXD. While auto parts stores will typically read your codes for free, they will not reset the light for you, and shops may charge more than $100 to do this. 

In the FIXD app, you can reset the light anytime you want for free. After performing the engine scan, go to the Details page and click the “Clear Engine Light” button. The light will turn off, and any codes stored inside your Prius’s computer will be cleared. If the light turns back on after a few miles of driving, the issue likely still exists.

FIXD Clear Check Engine Light

Diagnose Your Toyota Prius Check Engine Light with FIXD

If the check engine light turns back on, use FIXD to get detailed engine diagnostics, plain English code descriptions, issue severity warnings, and so much more. Learn more about the FIXD Sensor and mobile app today!

FIXD Research Team

At FIXD, our mission is to make car ownership as simple, easy, and affordable as possible. Our research team utilizes the latest automotive data and insights to create tools and resources that help drivers get peace of mind and save money over the life of their car.

Clear your check engine light in seconds

The FIXD Sensor and free app tells you why your check engine light is on in easy-to-understand terms and lets you clear it with the touch of a button. 


We’re here to help you simplify car care and save, so this post may contain affiliate links to help you do just that. If you click on a link and take action, we may earn a commission. However, the analysis and opinions expressed are our own.


About the Author

FIXD Research Team

FIXD Research Team

At FIXD, our mission is to make car ownership as simple, easy, and affordable as possible. Our research team utilizes the latest automotive data and insights to create tools and resources that help drivers get peace of mind and save money over the life of their car.

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