How to Troubleshoot a CVTby Alexander Eliot
A continuously variable transmission, or CVT, utilizes a system of tapered gears or pulleys to allow for a constantly variable gear ratio. This allows the engine to always operate at peak efficiency and performance, in contrast to conventional transmissions which have a set number of gear ratios from which to choose. Automobile CVTs are equipped with extensive electronic monitoring systems to ensure the transmission internals are operating properly. Therefore, you can troubleshoot virtually any extensive problem with your CVT by accessing the engine control unit diagnostic system.
Observe the vehicle gauge layout. Most problems with the CVT internals will activate the vehicle "check engine" light, often indicated by an illuminated engine symbol. Alternatively, some CVTs are programmed to flash one of the gear indicator lights, such as the overdrive light, when transmission problems occur.
Plug an engine diagnostic code reader device into the diagnostic access port, generally located underneath the driver's side dashboard area. The engine control unit, or ECU, monitors transmission malfunctions and stores an error code when malfunctions occur. If you do not have an ECU diagnostic reader, many automotive service centers offer free ECU code-reading service.
Study the error codes given to you by the diagnostic reader to troubleshoot the CVT. Each component malfunction features a unique error code, as well as a brief description of the malfunction. For a more detailed explanation of the error code, contact your vehicle manufacturer's service department.
Check the CVT fluid level. Access the CVT fluid dipstick, generally located in the lower engine compartment. Remove the dipstick and wipe off all excess fluid. Then, reinsert the dipstick and remove it once again. This leaves an accurate mark on the dipstick which indicates the fluid level. Compare the fluid level with the recommended level given by your vehicle owner's manual.
Blot a generous amount of the CVT fluid onto a clean, flat paper towel. Allow the fluid time to settle, then observe the color and consistency of the blot stain. Healthy CVT fluid will produce a consistently dispersed, light-brown blot. In contrast, worn fluid will produce a dense, dark blot on the towel. This is due to contamination of the CVT fluid, such as through oxidation. Flush and replace unhealthy fluid with new transmission fluid as recommended by your vehicle manufacturer.
Start the vehicle and shift the transmission between the various drive selections. If the gearshift feels hesitant, this indicates a problem with the gearshift or shift linkage components. However, if grinding or vibrations occur from the transmission itself upon gear changes, this indicates a problem with the transmission internals.
Accelerate your vehicle and observe the tachometer, which indicates rpm values. If the transmission struggles to increase or maintain the given rpm value, this indicates a problem with the internal CVT pulley system. For example, a slipping CVT belt will make it more difficult for the transmission to deliver the engine power to the wheels. Alternatively, a slipping belt and other internal CVT problems that hinder power delivery make the engine feel hesitant under heavy acceleration.