A difference between manual and automatic shift modes is useful diagnostic context. It does not prove the mechanical gearbox is healthy or the TCU is faulty. The requested gear, operating load and control strategy differ between the two modes.
Describe the actual shift problem
State whether automatic mode delays a shift, changes harshly, hunts between gears or selects an unexpected ratio. Record road speed, temperature and whether the same gear transition behaves differently when requested manually. Avoid testing aggressively or distracting the driver with logging equipment.
Include engine faults because transmission operation may depend on information from other systems. Ask the workshop to compare relevant requests and responses using the correct vehicle information. Do not reset adaptations before preserving the baseline unless the diagnostic procedure requires it. A useful report explains which transition was tested and which evidence supports the repair recommendation, rather than simply labelling automatic mode as a software fault.
Related help
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