1. Delayed gear engagement: This is one of the most common signs of transmission filter failure. When your filter is clogged or damaged, it may cause delayed gear engagement and even cause your car to shift out of gear.

2. Strange sound: The transmission should run quietly, so if you hear whistling, buzzing, or other abnormal sounds, it may be the sound from the transmission filter.

3. Smoke from exhaust pipes: If there is a problem with your car's transmission filter, you may notice smoke from the exhaust pipes. This is usually a sign of filter blockage, which may cause your car to overheat.

4. Unsmooth gear shifting: If your car's gear shifting is not smooth, it may be time to check the transmission filter. It may cause gear slippage and other shifting issues, such as random shifting of the gearbox.