What Causes an Automatic Transmission Car to Suddenly Fail to Shift Gears?
2 Answers
Automatic transmission failing to shift gears may be due to gear lock or incomplete braking when parking, directly shifting into P gear causing gear braking instead of brake braking. Additionally, if the entire vehicle cannot power on, the automatic transmission's self-protection mechanism may also prevent gear shifting. The specific reasons are as follows: 1. Gear lock engaged; When driving, shifting from P gear to other gears, Japanese cars generally require pressing the shift lock switch, while German cars usually require stepping on the brake. The P gear also functions as a handbrake, preventing rollback on slopes below 15 degrees, but steeper slopes require the handbrake. 2. Other reasons: P gear lock mechanism stuck and unable to reset; shift solenoid valve damaged, unable to complete shift commands; gear linkage damaged or broken; control computer malfunction.
I've been repairing cars for decades, and there are usually a few key points when an automatic transmission vehicle can't shift gears. The most common issue is the brake pedal not being fully depressed, preventing the shift lock mechanism from releasing. If stepping firmly doesn't work, then check the transmission fluid level and condition: low or deteriorated blackened fluid can reduce oil pressure, causing internal valves to stick. Electronic components also frequently malfunction, such as the gear position sensor sending false error signals or the control module failing due to low battery voltage. I recommend stopping immediately to inspect—start the engine and lightly press the brake to listen for feedback sounds. Develop good habits like regular fluid changes to avoid breakdowns on the road. Once, a driver ignored overheating fluid, leading to hydraulic system failure and nearly causing an accident. These small details truly can't be overlooked.
