What is the fault when an automatic transmission cannot upshift?
3 Answers
Possible causes for an automatic transmission's inability to upshift include improper adjustment of the throttle cable or throttle position sensor. Below is relevant information about automatic transmission upshift failure: 1. Other potential fault causes: (1) Governor malfunction or oil leakage in the governor oil circuit. (2) Vehicle speed sensor failure. (3) Malfunction in 2nd gear brake or high-gear clutch. (4) Stuck shift valve or gear position switch failure. 2. Diagnosis and troubleshooting methods: (1) Sensors affecting shift control include: throttle position sensor, vehicle speed sensor, etc. Check fault codes to identify causes. (2) Inspect the vehicle speed sensor. Replace if damaged. (3) Check gear position switch signals. Adjust or replace if abnormal. 3. Important notes: Automatic transmissions require timely fluid replacement, ensuring complete drainage of old fluid. Strictly control fluid quantity during refilling. After clutch or brake burn-out, promptly clean the torque converter hydraulic system which has two inlet ports, one located at the bottom of the control valve body.
When encountering an automatic transmission that won't upshift, my experience shows the problem usually lies with transmission fluid or electrical components. Low fluid level or contaminated fluid can cause hydraulic signal transmission failure, affecting gear changes. Sensor failures are also common, such as malfunctioning vehicle speed sensors or incorrect gear position signals, leading the control module to issue erroneous commands. Mechanical issues like clutch wear can cause power loss, but I recommend owners first perform basic checks: open the hood to inspect if the dipstick level is normal - if the fluid appears dark brown, change it immediately. If the fluid is fine, using a diagnostic tool to read trouble codes can save time. Don't neglect routine maintenance; regular fluid changes every 40,000 kilometers prevent minor issues from escalating. Delaying repairs can lead to four-figure repair bills - definitely not worth the cost.
I've been driving automatic transmission cars for over a decade and have experienced the embarrassing situation of the car not upshifting. Driving in the city with high RPMs but no gear change, it felt like driving a tractor. Looking back, it might have been an oil quality issue—I hadn't changed the transmission oil for too long, and it became too thick, blocking the signals. Or it could have been due to dust accumulation on the throttle position sensor, which a simple cleaning could fix. I've also heard that a short circuit in the control wiring harness can cause this fault. What car owners can do is simple: regularly check the oil level and top it up if it's low; when driving, avoid slamming the accelerator and be gentle to protect the car. If symptoms appear, immediately slow down and pull over to prevent the engine from overheating and blowing up. Minor issues can be fixed for just a few hundred bucks, but delaying until a major repair is needed would be a huge loss.
