A car that wont shift is stuck in limp mode, has a hydraulic problem, or has a mechanical failure inside the transmission. Catching it early can save thousands. Here are the most likely causes ranked by how often they turn out to be the problem.
Without enough clean fluid, the valve body cannot build pressure to shift. Always the first thing to check.
Each gear has a solenoid that directs fluid. A failed solenoid leaves the trans stuck in one gear or unable to upshift.
The ECM uses input/output speed sensors to time shifts. A failed sensor puts the trans in limp mode (usually 3rd gear only).
Wear or stuck valves in the valve body cause skipped, harsh, or missing shifts. Often paired with multiple solenoid codes.
A broken or misadjusted shifter cable means the gear selector and trans do not match. Common on older cars.
The car is making grinding or whining noises when in gear, you smell burnt fluid, or the trans will not shift at all and is leaking. Continuing to drive can turn a $500 solenoid into a $4000 rebuild.
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Limp mode. The ECM detected a serious fault and locked the trans in a safe gear (usually 3rd) to prevent damage. Scan codes immediately.
Yes. The valve body needs full pressure to engage clutches. Low fluid = low pressure = missed or no shifts.
Fluid: $150-$400. Solenoid: $300-$800. Valve body: $700-$1800. Rebuild: $2500-$5000.
Brake shift interlock failure, blown brake light fuse, or a broken shift cable. Use the manual override (small slot near shifter) to release it temporarily.
Yes, short distances at low speed to get to a shop. The trans is protecting itself - do not push it hard.