What is the maintenance case for an AMT transmission that does not upshift?
4 Answers
AMT transmission does not upshift maintenance case refers to a situation where the automatic transmission can only shift up to 1st gear during driving, and cannot shift to 2nd gear or higher gears; or it can shift to 2nd gear, but cannot shift to 3rd gear or overdrive. In such cases, it is necessary to seek professional repair from a 4S shop technician. Below is a relevant introduction to AMT transmissions: Overview: AMT is developed based on manual transmissions, retaining the gear-shifting structure and clutch of manual transmissions. The operations required for manual transmissions, such as pressing the clutch and selecting gears, are performed by an automatic control mechanism managed by a computer in AMT. Therefore, AMT essentially uses a computer system to operate the clutch and select gears. Technical Core: The core technology of AMT is microcomputer control, where the level and quality of electronic technology directly determine the performance and operational quality of AMT. Taking Magneti Marelli, the largest supplier of AMT, as an example, the AMT system design is completed through computer-controlled hydraulic shifting assistance systems, with components including pressure storage tanks, solenoid valves, etc.
A few days ago, I repaired a car with an AMT transmission that wouldn't upshift. The owner reported that the engine revs surged when pressing the accelerator, but the speed didn't increase. After connecting the diagnostic tool, we found a fault code indicating insufficient hydraulic pressure. We conducted a four-step inspection: first, we checked the hydraulic fluid level and found it was low; then, we inspected the pipelines and discovered a leak in the return line connected to the control unit; next, we examined the solenoid valves and found one of the valve cores was stuck; finally, we noticed that the clutch position sensor's feedback signal was drifting. The car's maintenance records were incomplete, and the transmission fluid hadn't been changed for 5 years. The solution was to replace the seals, clean the solenoid valve, and recalibrate the sensor. A reminder to everyone: AMT transmissions require fluid changes every 60,000 kilometers as per the maintenance manual, as deteriorated fluid can affect hydraulic control precision.
I personally encountered an issue where the AMT wouldn't upshift, as if stuck in 1st gear when in D mode. After towing it to the repair shop, they found unstable power supply voltage to the transmission TCU. The mechanic explained that AMT upshifts rely on the coordination between hydraulic actuators and the electronic control system, with common failure points including: misaligned clutch actuator mechanisms, clogged solenoid valves, insufficient oil pressure due to pump wear, and missing sensor signals. Last time, my car had a signal interruption caused by corroded wiring harness connectors. It's recommended to check the sealing condition of transmission connectors during every maintenance service, and to immediately inspect electrical connection points after driving through water. Simple fault code reading can pinpoint 70-80% of issues.
AMT transmission failure to upshift frequently occurs in high-mileage vehicles. Common causes include: stuck spool valves in the hydraulic control unit obstructing oil passages; stepper motor deviation in clutch actuators; wear pits on selector fork shafts; and TCU program malfunctions. In one case I handled, a taxi couldn't engage higher gears due to excessive fork shaft wear. Typical repairs involve cleaning oil circuits, recalibrating actuators, and replacing worn components. Drivers should monitor for abnormal noises or jerking during gear shifts - proper AMT shifting should be smooth and silent.
