AT Oil Temp Subaru Light Flashing: Meaning, Causes, How To Fix

by Conner Mckay

Owning a Subaru is a remarkable experience for any car lover. From the iconic WRX STI to the capable Forester, this Japanese manufacturer has been able to capture the imagination of gearheads around the world. But, there is one question that is commonly asked by owners of these Japanese cult classics. That is “what is AT oil temp Subaru?” Today, we hope to answer that exact question.

Some of you may already know that today’s topic is related to Subaru’s transmission system. After the engine, the transmission is perhaps the most important system in your vehicle. So, it is important that you have a proper understanding of how it works.

Today, we’ll tell you everything you need to know about the AT oil temp warning, as well as the Subaru transmission system overall. We guarantee that Subaru owners and non-Subaru owners alike would find this article very interesting. So, without further ado, let’s begin!

Car Transmission

Before focusing our attention specifically on the AT oil temp Subaru warning light, let’s focus our attention on the system that it is related to. As you might have already guessed, AT stands for automatic transmission. Do you know how an automatic transmission works?

The history of automatic transmissions runs all the way back to 1921. This was the year that Canadian engineer Alfred Horner Munro first made this innovation. Since that day, automatic transmission has become a popular feature among vehicle owners.

at oil temp subaru

It makes driving easier by eliminating the need to shift gears (fun fact, go check out our explainer on how to shift a motorcycle), while also improving overall benefits performance.

At its core, automatic transmissions use hydraulics to transfer engine power to the vehicle’s wheels. It is a complex system that consists of multiple components such as the,

  • Torque Converter
  • Clutch Pack
  • Planetary Gear Set
  • Oil Pump
  • Brake Band
  • Output Shaft (to learn more, check out our guide on how to replace transmission output shaft seal)
  • Oil Pan
  • Valve Body
  • Transmission Fluid

Let us go through each component and see what they accomplish inside the automatic transmission.

1. Torque Converter

In order for an automatic transmission to work, it has to be connected to the engine. This is where the torque converter comes in. So, what is a torque converter? It replaces the clutch by performing the same functions without any driver inputs.

For an automatic transmission to shift properly, it has to be disconnected from the engine for a brief period of time. Otherwise, the gears could snap and cause massive damage to the engine. Sounds familiar? That’s because this is the same thing that happens when you depress the clutch in an automatic transmission.

However, there is one major difference in the way in which these two systems work. The clutch connects the engine to the transmission system through mechanical means. On the other hand, the torque converter uses transmission fluid to connect the two components.

If you’d like to learn more, do check out our explainers on the symptoms of a bad torque converter, in addition to the typical torque converter replacement cost.

2.  Clutch Pack

An automatic transmission has to select different gear rations by itself. This is where the clutch pack which is another important component of the automatic transmission, comes in. It is used for maintaining the output gear ratio.

The clutch pack is composed of several plates, which are compressed together. Several of these clutch packs lock together once they receive oil pressure from the valve body. In order to change gear ratios, the amount of oil pressure has to vary.

3. Planetary Gear Set

A manual transmission has a set of multiple gears that come together to make up the gearbox. However, this is not the case with automatic transmission. Here, you can find one or more planetary gear sets.

A planetary gear consists of three sets of gears. The main one located at the center of the planetary carrier is called the sun gear. The second set is called the planetary gears, while the other gears mesh between the two.

4. Oil Pump

Automatic transmissions come with an oil pump that pumps transmission fluid from the transmission pan to the valve body. There, the valve body directs transmission fluid to all other components as needed.

The transmission system oil pump is notorious for failures. Although it is not overly complicated in its operation, the proper functionality of this component is essential for the automatic transmission to shift through the gears as intended.

5. Brake Band

The main responsibility of brake bands is temporarily holding the planetary gears. This allows the automatic transmission to shift through the gears smoothly, by allowing engine RPM to line up with the gear ratio before shifting up or down.

The brake bands are activated with a piston. This piston squeezes the band around a drum, similar to the action of drum brakes.

6. Output Shaft

Most gearheads consider the output shaft as the most complex part of an automatic transmission. One end of the output shaft is connected to the driveshaft (to learn more, check out our explainer on the drive shaft center support bearing replacement) through a universal joint, while the other is connected to the transmission itself.

7. Oil Pan

The transmission oil pan should not be confused with the engine oil pan, as they are two different components. However, both these parts function in a similar manner.

The transmission oil pan is responsible for holding excess fluid to be used when needed.

at oil temp subaru

Most vehicles have either an internal fluid filter attached to the oil pan as well.

Furthermore, it is important to note that this is one of the most troublesome of the transmission system as well. The gaskets that seal the transmission are notorious for premature failure.

8. Valve Body

The valve body acts like the ECU of the transmission system. It is what directs fluid pressure from the oil pump to all of the transmission components. Simply put, the valve body is the most important component of an automatic transmission system.

Modern automatic transmission valve bodies are controlled through sensors. These sensors work together with the Transmission Control Module to make sure that your vehicle shifts gears as intended. Its complexity is also the reason why valve body replacement costs tend to be very expensive.

9. Transmission Fluid

Last but not least, we have to take a look at the transmission fluid. It acts as the lifeblood of your transmission system. Not only does it lubricate the transmission system, but it is responsible for cooling purposes as well. Helping to maintain fluid pressure inside the transmission system is another responsibility of this liquid.

Now that you know all about the internal components of an automatic transmission, let us shift our attention to the Subaru AT oil temperature warning.

AT Oil Temp Subaru

Before learning how to fix the AT oil temperature warning, let us ask you a question? Do you know what system triggers it?

If you guessed “automatic transmission oil temperature control system” you deserve a pat on the back. Subaru manufactures this system to give off the AT oil temp Subaru warning when it detects any failures with the transmission system’s operations.

Several causes may lead to the oil temperature warning light turning on in your Subaru. They are,

  • Low Transmission Fluid Levels
  • Solenoid Issues
  • Using The Wrong Transmission Fluid
  • Extreme Temperatures

Let us go through these issues one by one to better understand the risks they pose.

AT Oil Temp Subaru Causes #1 – Low Transmission Fluid Levels

Depending on the make and model of a vehicle, an automatic transmission takes anywhere between 4 to 17 quarts of transmission fluid. However, if the vehicle is running low on transmission fluid, it will cause the system to overheat.

Leaks are the main cause of your vehicle running low on transmission fluid. As the transmission consists of many parts, there are many places where the fluid can escape through. The transmission pan gasket, seals, fluid lines, and torque pump are some places where the fluid is known to leak through.

In addition to the AT oil temp warning light turning on, there are several other symptoms that indicate low transmission fluid levels. Strange noises coming from the transmission are one such symptom. If you hear whining or humming sounds when the transmission is shifting through gears, it might be time to top up the fluid level.

As we mentioned earlier, transmission fluid is responsible for lubricating the internals of the system. Low fluid levels lead to inadequate lubrication, which results in the internal components rubbing together and producing these strange noises.

Gear slipping and shifting issues are two other symptoms that are indicative of low transmission fluid levels. Proper transmission fluid levels are essential for gear synchronization, and without them, the vehicle won’t go into gears as designed.

AT Oil Temp Subaru Causes #2 – Solenoid Issues

Solenoids are responsible for controlling the transmission fluid flow into and out of the engine. It is an electro-hydraulic valve and failure of it leads to irregularities in the amount of fluid entering the system. Over time, solenoid issues can cause complete transmission failures as well.

Similar to low transmission fluid levels, there are symptoms that you can use to identify solenoid issues beforehand as well. The check engine light turning on, the vehicle not downshifting, delayed gear shifts, erratic gear changes, and the vehicle going into limp mode are some that come to mind.

If you suspect that your transmission has a faulty solenoid, we recommend taking your vehicle to a qualified mechanic. They will inspect the solenoid and determine whether it needs to be replaced. So, be wary of the symptoms of a bad shift solenoid, such as a bad transmission solenoid fuse, and consider a transmission solenoid cost.

AT Oil Temp Subaru Causes #3 – Using The Wrong Transmission Fluid

Just like gasoline, there are several types of transmission fluids for sale on the market. So, it is important that you choose the correct type for your specific vehicle. A few of the most common types of transmission fluids available on the market are,

  • Multi-Vehicle Synthetic
  • Dexron VI/Mercon V/ATF+4
  • CVT Fluid
  • Type F

Multi-vehicle synthetic transmission fluid includes additives that improve their longevity and performance. Furthermore, this type of transmission fluid is suitable to be used on a wide variety of vehicles. As the name suggests, manufacturers formulate multi-vehicle synthetic transmission fluid utilizing synthetic base oils.

On the other hand, transmission fluids like Dexron VI, ATF+4, and Mercon V are licensed products made for large vehicle manufacturers – specifically Ford, GM, and Chrysler. These transmission fluid varieties come with friction modifiers that help with reducing friction inside the system.

Next, let us shift our attention toward CVT transmission fluid. These are specifically designed to be used with continuously variable transmission systems.

fluid type

CVT transmissions have gained popularity in recent years, mainly due to the fuel efficiency improvements they offer. In fact, 20% of all new cars on sale today come equipped with CVT transmissions.

Finally, we have Type F automatic transmission fluid. This transmission fluid type saw mainstream popularity before the 1970s. Type F fluid was mainly used in Ford vehicles, and doesn’t contain any friction modifiers.

Depending on the make and model of your vehicle, the manufacturer would recommend a specific type of transmission fluid to use with it. These fluids aren’t universal, so using the wrong type of transmission fluid can cause the AT transmission fluid to turn on.

AT Oil Temp Subaru Causes #4 – Extreme Temperatures

Operating your vehicle in extremely high temperatures can also result in the AT temp warning light turning on. To avoid this from happening, make sure that you let your vehicle adequately cool down (make sure you know how long does it take for a car to cool down) and park it in a shaded area to avoid transmission overheating.

Subaru Oil Light

In addition to the AT oil temp warning light, there are some other warning lights associated with Subaru vehicles as well. They are,

  • Rear Differential Temperature Warning
  • Low Oil Level Indicator
  • Low Oil Pressure Warning

Subaru Oil Light #1 – Rear Differential Temperature Warning

Some high-performance Subaru models like the WRX STI with an all-wheel-drive system come equipped from the factory with a rear differential. And, they come with a warning light dedicated to this system as well. If the rear differential overheats, not only does it damage the part itself, but it can cause engine damage as well

When the rear differential overheats, the vehicle directs the maximum amount of torque to the front wheels. This overrides any settings set by the user and significantly affects the vehicle’s performance characteristics.

We previously mentioned that transmission overheating can happen due to the lack of fluid in the system. The same applies to the rear differential as well. The interior of this part houses differential oil. This oil lubricates the metal components of the interior, preventing them from impacting each other.

Over time, the differential oil breaks down, losing its lubricating ability in the process. This is when the overheating issues start to rear their heads. If the rear differential temperature warning light of your Subaru has turned on, park your vehicle at a safe spot and let it cool down. After that, you might want to look into a rear differential fluid replacement.

Subaru Oil Light #2 – Low Oil Level Indicator

The low oil level indicator light has the shape of an oil can and will turn on when there is not enough motor oil inside the engine. If you spot this light on the dashboard, the best course of action is to top up the engine oil as soon as possible.

Running the engine with the low oil level indicator light on results in oil starvation. This issue causes catastrophic damage to engine internals and may require thousands of dollars to fix.

Subaru Oil Light #3 – Low Oil Pressure Warning

Low oil pressure is a catastrophic engine problem that should be remedied as soon as possible. When this happens, the internals of the engine won’t receive enough oil. It causes a whole host of issues such as overheating and strange noises.

If the low oil pressure warning light turns on while you are driving, pull over to the side of the road immediately. We don’t recommend driving your vehicle in this condition. Get it transported to the nearest auto mechanic to avoid any further damage.

Subaru AT Oil Temp Light Flashing

Some drivers have experienced the AT oil temp light of their Subaru flashing while driving down the road.

If this happens to you, immediately pull over to the side of the road. Driving your Subaru with this light flashing might destroy the entire transmission system.

AT Oil Temp Light Flashing Fix

The AT oil temperature issue is a bit complex for a home mechanic to diagnose and fix, and we recommend leaving it to the professionals. However, there are some minor fixes you can try that may hopefully get rid of this issue.

AT Oil Temp Subaru Fixes #1 – Let The Engine Idle

Letting the engine idle is one of the most basic fixes you can try. Let’s face it, all of us have done this at least once in our lives.

If you let the engine idle for an adequate amount of time, there is a high chance that the warning light will turn off. But, this doesn’t get rid of the core issue at all. Instead, the light will turn right back up when the transmission overheats once again.

AT Oil Temp Subaru Fixes #2 – Top Up The Transmission Fluid

The likelihood of the AT oil temp warning being caused by low transmission fluid is very high. As a precaution, you can try adding more automatic transmission fluid to the vehicle.

Before refilling the automatic transmission fluid, let the engine idle for a few minutes. This gets the transmission fluid warmed up to operating temperature, allowing it to seep out more freely. Then, remove the bolts attached to the transmission pan, and let the old transmission fluid run out.

Then, completely remove all bolts, and break the gasket seal using a screwdriver if needed. Clean the gasket surface, and remove the old transmission filter as well as the O-ring. After that, you can replace these components with brand-new ones before attaching a new oil pan gasket. Finally, reattach the oil pan, and refill the transmission fluid up to the manufacturer’s recommended level (to learn more, check out our guide on will a torque converter fill itself).

For extra safety, let the engine run for a few minutes and check for any fluid leaks. If no leaks are to be found, let the vehicle warm up to operating temperature, and you are good to go!

If you’d like to learn more about transmission fluid, do check out our guides down below:

Conclusion To AT Oil Temp Subaru

The AT oil temp Subaru warning light is related to the vehicle’s automatic transmission system. It can turn on due to a variety of issues, including low transmission fluid levels, extreme temperatures, a faulty transmission solenoid as well as filling up your vehicle with the wrong type of transmission fluid.


No matter the cause, it is important not to ignore this issue. If left unfixed, overheating can even cause complete transmission failure.

FAQs For AT Oil Temp Subaru

Here are some popular FAQs:

What Does AT Oil Temp Mean

The AT oil temp light is related to the automatic transmission system of your vehicle. It will turn on when the automatic transmission fluid has overheated. When this warning light turns on, you should stop your vehicle as soon as possible. If the light doesn’t turn off after a few minutes, it is time to call your mechanic.

How To Fix AT Oil Temp Subaru

Letting the transmission cool off is the best temporary fix for the AT oil temp warning light. Additionally, you may want to take a look at the automatic transmission fluid level as well.

What Causes Low Transmission Temp

Ideally, your transmission temperature should be between 175-200 degrees Fahrenheit. Anything below that figure is generally considered to be too low. Overheating is one of the most common causes of low transmission temperature. In addition, extreme cold weather is another well-known cause.

What Does Transmission Hot Idle Engine Mean

If the transmission system of your vehicle is running too hot, you may spot this warning symbol light up on the dashboard. This can be caused either due to the transmission overheating or suffering a cooling issue.

What Causes High Oil Temperature

Plenty of reasons can lead to the oil temperature of your vehicle getting too high. Using poor quality oil, compression leaks, cooling issues, and lubrication issues are some of the most common causes of high oil temperature.

What Does It Mean When The Transmission Light Comes On

Similar to the other warning lights we discussed, there are many reasons why this light might come on. Some of the most common causes include low transmission fluid levels, a blocked cooler, or complete system failure.

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