A continuously variable transmission or CVT uses a system of bevel gears or pulleys to allow a continuously variable transmission ratio. This allows the engine to always operate with maximum efficiency and performance, in contrast to conventional transmissions that have a fixed number of transmission ratios to choose from. Car CVTs are equipped with extensive electronic surveillance systems to ensure that the interior of the transmission is functioning correctly. Therefore, you can solve virtually any problem by accessing the diagnostic system of the engine control unit.
1-Observe the vehicle layout indicator. Most problems with the internal operation of the CVT will activate the “check engine” light, which is often indicated by an illuminated engine symbol. Also, some CVTs are programmed to blink one of the speed indicator lights as overdrive light, when transmission problems occur.
2-It connects a code reader for a diagnosis of the motor to the diagnostic port, which is usually located under the instrument panel on the driver’s side. The engine control unit or ECU (for its acronym in English), monitors the transmission failures and stores an error code when these malfunctions occur. If you do not have an ECU diagnostic reader, many automotive service centers offer the free ECU code reading service.
3-Study the error codes thrown by the diagnostic reader to solve the problems of the CVT. Each component with faults includes a unique error code as well as a brief description of the fault. For a more detailed explanation of the error code, contact the service department of the vehicle manufacturer.
4-Check the liquid level of the CVT. Access the liquid level dipstick of the CVT, usually located in the lowest engine compartment. Remove the rod and clean all excess liquid. Next, reinsert the rod and remove the liquid one more time. This leaves a precise mark on the rod, which indicates the level of liquid. Compare the fluid level to the level recommended by the vehicle owner’s manual.
5-Dry a generous amount of CVT fluid with a clean, flat paper towel. Let the fluid settle and then observe the color and consistency of the stain. Good CVT fluid will produce a consistent, light brown scattered stain. In contrast, the spent liquid will produce a dark and dense spot on the towel. This is due to fluid contamination, such as oxidation. Empty and replace the damaged fluid with the new transmission fluid as recommended by the vehicle manufacturer.
You will need to
- A diagnostic reader for ECU
- A paper towel
- CVT fluid
- AA1 Car: Diagnosing Automatic Transmission Problems
- Continuously Variable Transmission Reference Guide (Reference guide for continuously variable transmission)
- ECROS Tech: The Prius “Continuously Variable Transmission” (“Continuously variable transmission” Prius)