Why does an automatic gearbox delay gear shifts?

If the gear changes in your automatic gearbox arrive late, or at the wrong moment, the car is telling you that something may be wrong. The causes range from the simple to put right to serious damage calling for a full rebuild. Below we go through the main reasons an automatic gearbox delays its shifts and the ways of dealing with each of them.

1. A low oil level or oil in poor condition

One of the most common causes of delayed gear changes is the wrong oil level in the automatic gearbox, or oil that is in poor condition. The oil is central to how an automatic gearbox works: it lubricates, it cools and it transfers power. When the level is too low or the oil is contaminated, gear changes start to arrive late.

2. Sensor and electronic faults

Modern automatic gearboxes are fitted with advanced electronic systems that control the whole shift process. Damage to the speed, oil pressure or temperature sensors can make the gearbox behave incorrectly, delayed gear changes included. Faults in the transmission control module (TCM) can be responsible for the same kind of symptom.

3. Mechanical damage

Worn or damaged mechanical parts of an automatic gearbox — the clutches, the friction plates or the torque converter — can also cause delayed gear changes. These are the parts responsible for smooth transitions between the individual gears, so damage to them shows up as delays or as a gearbox that no longer works correctly.

4. Solutions and repair

Depending on the cause, the problem may call for different repairs:

• An oil and filter change – where the trouble comes from the condition of the oil.
• Repair or replacement of damaged sensors and electronic components.
• A rebuild or replacement of damaged mechanical parts of the gearbox.
• Reprogramming or repair of the transmission control module (TCM).

Summary

Delayed gear changes in an automatic gearbox are not a problem to ignore. Recognising the cause early and acting on it can prevent more serious damage and expensive repairs. If you are seeing symptoms like this in your car, we recommend consulting a professional workshop that specialises in automatic gearbox repair.

See also

• Why does an automatic gearbox jerk? — jerking during shifts is the most common first sign of worn clutches and contaminated fluid.
• Why does an automatic gearbox enter limp mode? — limp mode locks the gearbox in a single gear and usually follows earlier symptoms left unattended.
• Gear lever stuck with the brake pressed — a lever that will not leave P is normally a shift-lock fault rather than a gearbox failure.