3 Reasons Why Prius Red Triangle Appear

Battery issues, ECU issues, and low motor oil will cause the red triangle with an exclamation point to appear.

My Prius’ red triangle with exclamation point has appeared

The modern Prius has many warning signs. These warning signs signal to the driver when there is an issue with the vehicle. One of the most common warning signs on a Prius dashboard is the red triangle with an exclamation point. 

This warning sign functions as the check hybrid battery light. There could be a multitude of reasons ‌ the red warning light appears, but most of the reasons are because of the hybrid battery. 

Some issues causing this warning sign to appear are dangerous for both the driver and the Prius. 

Prius Drivers have given the triangle with an exclamation mark a nickname: The Triangle of Death.

What are the most common reasons that will cause the Prius’ red triangle warning light to appear?

Battery and ECU issues

If you have never heard of an ECU, it is a critical part of all vehicles. Its full name is the engine control unit. Some other manuals call the ECU the PCM, which is another name for the Powertrain control module. 

The purpose of the ECU is to monitor and connect many of the functions and parts and data in an engine and deliver the information to the right parts of the engine.

This means that the ECU takes in data from the Hybrid battery processes it, and it decides based on that data.

When the ECU experiences a glitch or is not processing data correctly, all kinds of things can go wrong.

The primary function of the ECU for the Hybrid battery is to monitor the internal temperature of the battery and monitor the amount of charge left in the battery.

So in the ECU cannot do these things, the battery can overheat or the battery can run out of charge.

Low oil pressure

Low oil pressure is one reason the Prius’s red triangle of death appears. Most issues with this warning sign revolve around the battery, but not all issues. So what does low oil pressure mean?

When the Prius experiences low oil pressure, it can send the engine into a state of shock. The vehicle’s engine will seize up. That could be a few reasons motor oil is not getting to the places it should be in your vehicle. 

The number one reason is that there is no oil left in the oil tank. Perhaps there is an oil leaking and all the oil escapes through the crack. Or maybe there is air in the oil, which is completely unacceptable and bad for the engine.

Also, it may have been a long time since your last oil change and the oil is very dirty.

How to test your hybrid battery for issues

It can devastate a driver to see the red triangle of death. Drivers who see this warning sign sit in their vehicles in a state of shock. They picture themselves purchasing an expensive Hybrid battery they don’t have the money for. But all is not lost when this triangle appears.

There are ways to test the Prius’s battery’s health and see if the battery is the actual problem. If you have the right tools, you can even test them at your home. You won’t have to take it to a mechanic.

First, purchase an ODB reader. They are available on Amazon or through the Toyota shop. You can also find them at an auto body store.

Now, locate the ODB port. It is usually above the brake pedal. Plug the ODB reader into the port. It should light up when it is in the port.

If you see a blue flashing light, that is the Bluetooth mic. Pull out your phone and sync your smartphone to the ODB reader. The ODB reader will prompt you to download and open the ODB app.

Select the reader, and the next screen will show you the Battery Monitor. All the information from the ODB reader is now on your smartphone.

There will be many categories on the battery monitor, but the ODB reader app will show you if there is something wrong with the vehicle or if the voltage is poor.

You can use the ODB reader app on your phone to perform a full battery test and the life expectancy test.

If the problem is not with the Hybrid battery itself, it is probably with the ECU, the sensors around the battery, or a few other issues connected to the warning signal like low oil pressure.

Cost of a new hybrid battery

Let’s face it, the cost of a brand new Hybrid battery is expensive. Be prepared to pay anywhere between $2,000 and $8,000. 

The price depends on the year, the make, and the model of the Prius. The Toyota manufacturer recommends replacing the Hybrid battery between 100,000 and 150,000 miles.

Many hybrid vehicles actually do last past the 100,000 miles mark.

Can you replace a hybrid battery yourself?

Replacing your Hybrid battery is not a straightforward task. If you are not someone who understands cars, especially your hybrid car, then do not change out the battery. 

Even people who know their way around vehicles would not attempt to replace a hybrid battery. First, the Hybrid battery is not where a normal vehicle battery would be. Instead, it is in the trunk below the back seats.

It Is far easier to pay a mechanic to replace the battery than to take it upon yourself to remove and replace your battery.

When you hire a mechanic, they will have the knowledge to remove all the plastic, metal, and seats, pull out the battery, replace the battery, and put your vehicle back together again.


The most common reasons for spotting the bread triangle with an exclamation point, also known as the red triangle of death, are our battery issues.

However, oil issues can also make this warning sign appear on your vehicle’s dashboard. If you have an ODB reader, you’ll be able to test the health of the Hybrid battery yourself.

  • Eric Williams

    I'm the founder of Daily Car Tips. I wrote articles in the automotive industry for more than 10 years, published in USA and Europe. I love sharing my knowledge and insights with fellow enthusiasts. Join me on this journey as we explore the exciting world of cars together!