Low transmission fluid can cause gear-shifting issues in a vehicle, which can cause the ECM or TCM to trigger the Overdrive Light as a warning message – as it detects something’s wrong with the transmission system.
The automatic transmission system has a lot of internal moving parts that can overheat under load. If not prevented, this heat can wear down these parts quickly, resulting in transmission failure.
This is where the transmission fluid comes into the equation.
It circulates through the transmission system, absorbs the heat from those moving parts, and then flows through the transmission cooler. The cooler’s fins take in this heat and dissipate it into the surrounding air with the help of a cooling fan – to cool down the fluid.
Once the fluid is cooled down, the whole process repeats.
However, heat dissipation is not the only benefit of the transmission fluid. It also lubricates the internal parts of the system (such as gears, clutches, and bearings) to reduce friction and wear.
Lastly, it prevents the buildup of deposits in the transmission system, thereby protecting the components from corrosion and oxidation.
What is Overdrive?
Overdrive is a feature found in many vehicles with automatic transmissions.
You can think of it as an extra higher gear in your transmission. If enabled, overdrive allows the vehicle to maintain the same speed while the engine operates at a lower RPM than before (Revolutions Per Minute) due to a higher gear ratio.
Due to lower RPM, the overdrive enables the engine to consume less fuel as it doesn’t have to work as hard as before -thereby increasing the fuel economy.
Another advantage of an engine operating at low RPM is the less stress on its internal parts, which reduces the maintenance cost and extends its overall lifetime.
In older vehicles, overdrive can be enabled or disabled manually with a button. In newer models, though, the ECM automatically engages and disengages it, depending on the driving conditions.
Can Low Transmission Fluid Cause Overdrive Light to Flash?
The overdrive light is one of the many warning messages that appear on the vehicle’s dash screen under different circumstances.
It’s usually written as ‘O/D OFF’ and indicates that the overdrive function is not working. In normal circumstances, it appears when you manually toggle the overdrive switch to the off position.
But if this light appears when you haven’t done anything, it indicates something’s wrong with overdrive or the vehicle’s transmission system.
There can be many reasons behind this warning message, including the low transmission fluid.
As discussed above, low fluid can cause various issues in the transmission system, such as low fluid pressure (required for activating overdrive solenoid), erratic gear-shifting, transmission overheating, etc.
These problems can cause the Engine Control Module (ECM) or Transmission Control Module (TCM) to trigger the overdrive warning light on the dash screen.
Symptoms of Low Transmission Fluid
Below are some of the common signs of low transmission fluid.
Noises From Transmission
Low fluid can increase the friction between the internal parts of the transmission system. This increased friction, in turn, can cause those parts to produce grinding, humming, or whining noises when moving.
The low amount of transmission fluid can also cause the transmission to overheat and burn the remaining fluid, resulting in a burning smell from the transmission system.
Transmission fluid is also used to maintain the hydraulic pressure to engage and disengage gears.
Therefore, if the fluid level gets low, the transmission system’s ability to engage or maintain proper gear engagement will reduce, resulting in slipping gears.
Under this condition, you may notice that the vehicle hesitates during acceleration or engine RPMs increase without an actual increase in speed.
Slow Gear Engagement
Another issue caused by insufficient hydraulic pressure is slow gear engagement.
As low transmission fluid reduces this pressure, it takes more time for the transmission to engage gears.
Inability to shift Gears
If the fluid level goes too low, the vehicle may not shift gears at all.
‘Transmission Over Temp’ Warning Message
Many vehicles will have a ‘transmission over temp’ warning message on their dash screen due to overheating caused by the low transmission fluid.
What Causes Transmission Fluid to Get Low?
Some of the common reasons behind low transmission fluid include:
Different transmission system parts, such as cooler lines or the transmission pan, can crack or damage over time. These cracks/damage can cause the fluid to escape the system.
Faulty Seals and Gasket
The transmission system relies on seals and gaskets to prevent fluid leaking. These seals/gaskets can crack over time due to wear, heat, and pressure, which cause the fluid to leak out of the system.
Torque Converter Failure
In some cases, the torque converter’s seals, gaskets, or housing can be damaged due to wear or an internal failure, leading to fluid leaks. This leakage, in turn, can cause the transmission fluid level to get low.
Many times, you get a low transmission due to improper vehicle service.
During the servicing, the mechanic’s job is to drain the old fluid, replace the transmission filter (if it’s contaminated), and then refill the system with new fluid.
Therefore, if they don’t pay attention and somehow fail to add the required amount of new fluid, its level will be low.
How to Fix Low Transmission Fluid?
The most obvious fix for low transmission fluid is simply adding more fluid. That’s because internal components of the transmission system can get damaged and leak small amounts of this fluid over time.
Here’s what you need to do to refill the fluid:
- Park your vehicle on a flat surface and engage the parking brake.
- Locate the transmission dipstick, pull it out, and wipe it clean with a cloth.
- Put the dipstick back entirely and pull it out again after some time.
- Check the transmission level on the dipstick. It will have some markings to show the min and maximum levels of the fluid.
- If the fluid is below the minimum level, add new fluid in a smaller amount and check the level again.
- Do this until the level is above is minimum mark.
- Make sure that it doesn’t cross the maximum mark either, as it can harm the transmission.
- Once you’re satisfied, put the dipstick back and tighten it securely.
If the O/D light is flashing in your vehicle for no apparent reason, you should try to find its true cause. That’s because it indicates that something’s wrong with the overdrive system.
In case you’ve refilled the transmission fluid but this light is still there, look out for other issues in the transmission system, such as damaged/corroded electrical connections, solenoid failure, sensor issues, etc.
Frequently Asked Questions
How Many Miles Until a Transmission Goes Out?
A transmission system can generally last 100,000-200,000 miles with proper maintenance.
Can Low Transmission Fluid Cause Surging?
Low transmission fluid can cause issues like insufficient hydraulic pressure and erratic gear shift, which can result in the vehicle surging. If your vehicle is surging forward before falling back to normal speed/acceleration, low transmission fluid can be the reason.
Can Low Transmission Fluid Cause the Check Engine Light to come on?
Low transmission fluid can cause gear slippage, which can result in the Check Engine light coming on the dash screen.
Does Overdrive Damage Transmission?
Using overdrive in specific situations, such as towing heavy loads, driving uphill, or in stop-and-go traffic, can put excessive stress on the transmission and can result in damage.
How Do You Know If Your Transmission Fluid Is Low?
If you’re in doubt about the low transmission fluid level, check for different symptoms associated with it. These include delayed gear engagement, rough gear-shifting, whining/humming noises from the transmission, “transmission over temp” message on the dash screen, etc.