Short answer: The most common signs of a failing automatic gearbox are slipping, harsh or delayed shifts, a jolt into Drive or Reverse, whining, a burning smell, red or brown fluid leaks and limp mode. Most start small, so a scan and fluid check early can prevent a full rebuild.
1. Slipping
The engine revs rise but the car does not pick up speed to match, as if the gearbox briefly lost its grip. Slipping usually points to worn clutch packs inside the gearbox, low fluid, or a pressure problem in the valve body.
2. Harsh or delayed gear changes
A thump between gears, or a pause before the next gear engages, often comes from old fluid, a sticking solenoid in the valve body, or adaptation values that need resetting. Software and fluid issues are the cheaper end of gearbox repair, which is why it pays to check early.
3. A jolt when selecting Drive or Reverse
A clunk when you move the selector can be worn engine or gearbox mounts as well as an internal fault. A workshop can tell the two apart quickly.
4. Whining, humming or buzzing
Noises that change with road speed can come from bearings, the torque converter or the final drive. Noises that change with engine speed point elsewhere. Note when the noise happens before you bring the car in.
5. A burning smell
Overheated gearbox fluid has a sharp burnt smell. It means the fluid is breaking down and no longer protecting the gearbox properly. Stop driving hard and have it checked.
6. Red or brown fluid under the car
Automatic gearbox fluid is usually red or amber when fresh and darkens with age. A leak lowers the fluid level, and a gearbox running low on fluid can slip and overheat. Seals and pan gaskets are common leak points and are usually straightforward to replace.
7. Warning message and limp mode
If the gearbox detects a serious fault it may hold one gear to protect itself. Drive gently to a workshop. Carrying on as normal in limp mode can turn a sensor fault into internal damage.
What to do next
Get the gearbox scanned and road tested, and have the fluid level and condition checked. Many problems turn out to be electrical or fluid-related and are fixed without removing the gearbox. When the fault is mechanical, the gearbox has to come out for inspection and repair.
