Automatic transmissions rely on a pump to create internal fluid flow and pressure. The pump, built into the front of the transmission, is driven by the torque converter when the engine is running.

When the pump turns, it creates a vacuum that pulls fluid from the pan through the filter. Then the pump pressurizes that fluid and sends it to passages inside the transmission.

There are two common transmission pump designs: gear and vane. The gear-type is fixed displacement; it moves the same amount of fluid all the time. On the other hand, the vane type is variable displacement and adjusts oil output via a slider valve.

Pressurized fluid from the pump is critical to keeping the transmission cool, lubricated and working well. In other words, the pump is the heart of the transmission. And if it fails, it can cause many problems.

Signs of a failing transmission pump

These are some of the most common problems associated with a failing transmission pump:

• Noise: A failing transmission pump will often make a whining noise. Because the unit is driven by the engine, the sound usually increases as you accelerate.
• Transmission slippage: Transmission fluid is used to change gears as you drive. A weak pump may not produce enough pressure to operate the necessary components, resulting in transmission slippage.
• Check engine light: An onboard computer monitors transmission operation. The device may turn on the check engine light if it detects a problem caused by a bad pump.
• No movement in any gear: A totally failed pump will prevent the vehicle from moving in any gear.
• Fluid leak: A seal fits tightly around the area where the converter meets the pump. If the seal fails, fluid will leak at the front of the transmission.

How to fix the problem

The entire transmission and torque converter must be removed to access the pump. Because of this, any repairs are best left to a professional.

Sometimes, if a bad pump or front seal is addressed quickly, the issue can be fixed without rebuilding the transmission. But in most cases, problems with the pump will lead to damage in the rest of the transmission, requiring a rebuild or replacement.

If transmission repair is deemed necessary, the torque converter should also be replaced. The cooler lines will also need to be flushed, and a new filter must be installed.

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.