Staring at your dashboard while driving along and suddenly that ominous glowing orange “AT Oil Temp” warning light pops on. Uh oh, what’s going on?
Your mind races thinking about what damage could be happening under the hood. Luckily, in most cases it’s not an emergency if the Subaru AT Oil Temp light comes on, but you still shouldn’t ignore it.
So what causes the Subaru AT Oil Temp light to come on and how serious is it?
The short answer is – the AT Oil Temp light indicates the transmission fluid temperature is too high. It’s typically not a dire emergency, but still needs prompt attention to prevent eventual internal transmission damage.
In this detailed guide, we’ll demystify exactly what that cryptic AT Oil Temp light means, the common problems that trigger it to turn on, and how to diagnose and fix the issue yourself or with a mechanic.
By the end, you’ll have confidence in understanding the meaning of the Subaru AT Oil Temp warning and skills to troubleshoot it when that worrying orange light flicks on. Here’s everything drivers need to know:
Table of Contents
What Does The Subaru AT Oil Temp Warning Light Mean?
First, let’s decode what the AT Oil Temp symbol that illuminates on your Subaru’s dashboard actually means:
AT stands for the automatic transmission.
Oil Temp indicates the transmission fluid temperature is hotter than it should be for normal operation.
So in plain English – the AT Oil Temp light means the automatic transmission fluid is overheating above its optimal temperature range.
Transmission fluid is vital for lubrication, cooling, and hydraulic pressure in the gears, shafts, and clutches of your Subaru’s automatic shifting system.
When the AT fluid overheats, it can lose viscosity and lubricating properties leading to accelerated wear on internal parts. Think of it like your car’s transmission sweating – not a situation you want persisting for long without action.
The AT Oil Temp light serves as an early warning before permanent damage can occur inside the automatic transmission. But to prevent issues, you need to promptly diagnose and repair the root cause of the overheating fluid.
Next, let’s explore why your Subaru’s transmission fluid might be getting excessively hot and triggering the AT Oil Temp warning in the first place.
Why Does The Subaru AT Oil Temp Light Turn On?
Many drivers see the AT Oil Temp warning light and assume the transmission itself is broken. But in reality, there are a few common causes – some of which are simple fixes:
Causes of a Subaru AT Oil Temp Light Coming On
- Low Transmission Fluid Level
- Slipping Transmission
- Failing Transmission Cooler
- Faulty Temperature Sensor
- Clogged Fluid Cooling Lines
Now let’s dive deeper into each of these common culprits that could be the reason behind your illuminated AT Oil Temp light.
Low Transmission Fluid
One of the first things you should check when seeing the AT Oil Temp light is the transmission fluid level.
Automatic transmission fluid serves many crucial roles beyond just lubrication and cooling. Low fluid can affect shift quality, lead to slippage, and allow overheating to occur.
With Subaru’s sealed transmissions, checking the fluid level takes an extra step compared to most cars. The fluid level can only be checked accurately with the engine warmed up and running.
If your Subaru AT fluid is low, topping it off to the proper level on the dipstick can potentially stop the overheating issues and turn off the AT Oil Temp light.
However, low fluid level can sometimes point to an unseen leak or larger issue. So keep an eye out for the light returning even after topping off the fluid.
Does your Subaru seem to lag or delay shifting between gears? That’s a condition known as transmission slippage.
When internal clutch packs start to wear out, they begin to lose grip which causes slippage between shifts. This puts extra stress on components and all the excess friction generates additional heat.
If you’ve noticed new hesitant shifting, it could be overheating the fluid and triggering the AT Oil Temp light. Catching slipping early before severe wear can help save the transmission.
Faulty Transmission Cooler
Part of controlling transmission temperature is the job of the fluid cooler.
Subaru transmissions use an auxiliary cooler that circulates fluid to remove heat and regulate operating temperature. Issues like leaks, clogs, and insufficient cooling capabilities can all cause fluid overheating.
Replacing a damaged transmission cooler is one potential fix if you determine it’s the root cause of illumination of your AT Oil Temp light.
Bad Temperature Sensor
The AT Oil Temp symbol on your dashboard is triggered by a temperature sensor that monitors the automatic transmission fluid.
Like any sensor, it’s possible for the transmission temperature sender to become defective and inaccurate. This may activate the warning light even when fluid temperatures are in a normal range.
Faulty sensor wires damaged by vibration can also give incorrect readings. Fortunately, replacing a bad oil temp sensor is relatively inexpensive if diagnosed as the culprit.
Clogged Cooling Lines
Lastly, clogged transmission cooler lines can prevent proper flow and heat transfer of the fluid.
Over years of use, sediment build up inside the small rubber hoses can restrict circulation. Fluid that isn’t flowing or exchanging heat properly has a hard time staying cool.
Clogged cooler lines are more common on older, high mileage Subarus. Flushing debris from the transmission cooler system can restore proper flow and help lower fluid temperatures.
Alright, now that we’ve covered the most frequent causes, let’s talk about the step-by-step process for diagnosing and verifying why your Subaru’s AT Oil Temp light is on.
How To Diagnose & Fix An Illuminated Subaru AT Oil Temp Warning?
When your Subaru’s instrument panel lights up with the unsettling AT Oil Temp warning, follow these tips:
Step 1 – Check Transmission Fluid Level
Since low fluid is a prime suspect, start by checking the automatic transmission dipstick. The fluid should be checked only after warmup with a hot engine running. Add fluid as needed to reach the proper “hot” level on dipstick. This may resolve it if low levels were the culprit.
Step 2 – Scan For Transmission Trouble Codes
Connecting a scan tool to read transmission diagnostic trouble codes (DTCs) can provide insight into sensor or internal issues. Address any stored code concerns.
Step 3 – Transmission Fluid Flush & Cooler Line Cleaning
Flush debris and overheated fluid out of the system. Also backflush cooler lines to ensure no flow restrictions exist. New, clean fluid helps reduce heat.
Step 4 – Transmission Cooler Inspection
Visually check for leaks indicating a damaged cooler and physically check for clogs in the fin design. Replace if faulty cooler found.
Step 5 – Test Drive Vehicle
Operate the vehicle to determine if the conditions causing the warning light are still present after repairs.
By methodically following these troubleshooting steps, you can get to the root cause and remedy it before permanent damage can occur inside your Subaru’s automatic transmission.
If you already have a rough shifting or slipping transmission, then a rebuild or replacement may be required. But in many cases of AT Oil Temp light illumination, early intervention prevents further degradation and saves the transmission.
What To Do If Subaru AT Oil Temp Light Stays On?
If you’ve diagnosed the system and the Subaru AT Oil Temp warning persists or keeps returning, don’t continue driving with the light on or the problem could worsen.
Persistent overheating of automatic transmission fluid will significantly accelerate wear and eventual failure. Catch it soon and save your transmission.
But also don’t panic and assume you automatically need a rebuilt transmission if the light stays on. There are still steps you can take:
- Retest fluid level and get a second opinion from another shop on diagnostics.
- Consider installing an auxiliary transmission cooler to improve heat reduction.
- Use a heavier duty transmission fluid that withstands heat better.
- As a last resort, Remanufactured transmissions are an affordable alternative to full new transplants.
The key is not to delay and allowing excessive overheating damage to take its toll. Be proactive in diagnosing and correcting the issue triggering the warning light.
Subaru AT Oil Temp Light On After Transmission Service – Should I Worry?
A common concern is the AT Oil Temp illuminating immediately after a transmission fluid change or flush. Is this a sign of a bigger problem?
In most cases, it’s not an immediate cause for concern. Here’s why:
Fresh, new automatic transmission fluid can take some time to reach optimal operating temperature. Until it fully circulates and the friction modifiers activate, you may see the light.
Allow a few short drives to circulate the new fluid, and if temperatures level off, the light should extinguish itself and system will be fine.
However, if the light remains on consistently even with new fluid, then a larger issue is likely at play, and you should investigate deeper per our troubleshooting tips.
How To Reset Subaru AT Oil Temp Warning Light?
Once the underlying root cause is repaired, resetting the AT Oil Temp light is fortunately a quick process in your Subaru:
Reset Subaru AT Oil Temp Warning Steps:
- Turn vehicle ignition to the “On” position without starting engine
- Press and hold trip meter reset button
- While holding reset button, turn ignition to “Off” then release
- Restart engine and light should be cleared
This simple reset procedure will get rid of the nagging AT Oil Temp illumination after you’ve fixed the problem. Now let’s recap a few final tips about the Subaru transmission overheating warning light.
Subaru AT Oil Temp Light – The Bottom Lines
- Illumination means the automatic transmission fluid temperature is too high.
- Overheating fluid can cause internal transmission wear and eventual failure.
- Common causes include low fluid, slipping trans, bad cooler, faulty sensor, or clogged lines.
- Diagnose the root problem and repair it promptly to prevent lasting damage.
- Reset the warning light after addressing the underlying issue.
While seeing your Subaru’s AT Oil Temp warning light come on can give you a fright initially, in most cases it just indicates servicing some fairly affordable transmission system components, not a full rebuild.
With the knowledge of how to troubleshoot the problem accurately, you can take action and help prolong your Subaru’s transmission longevity.
Now you’re armed with an understanding of what the Subaru AT Oil Temp light means, what causes it, and how to properly diagnose and repair it. Never ignore it, but also don’t panic. With some proactive troubleshooting, you’ll have it back to normal in no time.