What are the fault diagnosis methods for automatic transmissions?
2 Answers
Automatic transmission fault diagnosis methods are: 1. After the engine is warmed up, shift into P or N gear, turn off the air conditioning, and check the idle speed. 2. Inspect the throttle position cable and sensor. 3. Check the quality of the automatic transmission fluid. 4. Shift into P or N gear and push the vehicle. 5. Check the P or N gear start switch. 6. Move the gear lever sequentially from P position to other positions to check if the shifting is smooth. The functions of the transmission are: 1. Change the transmission ratio to meet the traction needs under different driving conditions. 2. Enable reverse driving. 3. Interrupt power transmission. 4. Achieve neutral gear.
As a seasoned mechanic with over a decade of transmission experience, I've seen countless automatic transmission failures. Diagnosing issues follows a systematic approach. First, check the dashboard warning lights—especially that yellow gear symbol; if illuminated, there's likely an electronic control problem. Next, road-test the vehicle to assess shift quality: hesitation, delays, or unusual noises during gear changes. If RPMs suddenly spike during 3rd-to-4th gear shifts, suspect clogged fluid passages or worn clutch plates. Post-test, inspect the fluid—check dipstick levels and examine color/smell. Healthy fluid appears translucent pink; blackened fluid indicates friction material disintegration. Always scan for trouble codes, particularly monitoring solenoid data streams in valve bodies—like Volkswagen DSG's notorious solenoid sticking issues. Immediate action is crucial if you spot pan leaks or cooler seepage—low fluid can rapidly destroy planetary gear sets.
