Automatic transmission won’t shift into high gear

Automatic transmissions have already become popular among drivers. As a result of many advantages, the demand for these units is constantly growing. But these transmissions are more sensitive than manual types and are more prone to certain failures.

Being quite sensitive to improper operation of the unit, it may work incorrectly from time to time, and one of the causes is not shifting into a higher gear or not changing gears at all.

In such cases, the car owner has no choice but to try to solve the problem. But, first of all, you need to make sure that this fault is really related to the transmission.

Usually, one of the main causes due to which the automatic transmission does not shift into high gears or won’t change gears at all is often a lack of fluid in the system. As a rule, this is usually due to a worn-out oil seal of the unit, which is why the fluid leaks.

Many drivers are facing more of the problem of an automatic transmission that won’t shift into high gear, but this is related to why it does not shift gears in the first place.

Causes why automatic transmission does not shift gears

Depending on the car’s make and model, automatic transmissions may have some differences, but the main causes of shifting problems are common. 

Let’s start with the fact that one of the most common mistakes leading to this automatic transmission fault is a bad habit that drivers do very often.

This bad behavior is shifting to “D” drive mode without stopping when reversing. The same can be said for engaging the “R” when driving forward. This mistake will definitely lead to major faults in the automatic transmission, especially the one we are talking about.

Also, the lack of transmission fluid is another common cause, as I said above. Low fluid levels in AT may occur due to the following reasons:

  • Fluid leaks, because of worn-out oil seals. These bad seals are also caused by the use of chemicals or a poor-quality transmission fluid. Leaks can also be due to the wear and tear of the deflector caps, and here overheating is the main reason for this issue.
  • Vacuum corrector faults. Inside this device, there is a special membrane that reacts to the level of vacuum. If this membrane is bad, the transmission fluid will get into the car’s motor. In this case, the unit can operate for a long time even with a significantly reduced level of lubrication, but over time it will simply fail.
  • If the pipe that connects the automatic transmission to the oil cooler is broken, all the lubricant will leave the transmission in a few minutes, so the unit will simply stop working.

Also, transmission oil leaks can happen because of a bad AT fluid cooler that is not tightened enough. So, the transmission oil can get into the engine’s radiator, helped by the fact that its pressure is higher than the pressure in the cooling system.

Also when the engine is off, leaks of AT fluid can get into the coolant and this will form emulsions both in the engine and the transmission.

When antifreeze is in the AT, it will corrode the friction clutches. In this case, if the gears are not shifting, the problem can be solved by replacing the oil cooler. Also, it’s best to flush the automatic transmission and replace the fluid.

The symptoms of automatic transmission that does not shift gears

  • The automatic car drives only in reverse (R position). In this case, you need to replace the friction clutches, piston collar, clutch rings, or hydroblock valve is jammed.
  • The car will engage only in first and second gear due to bad friction clutches, wear of o-rings, and clutch malfunctions.
  • The transmission won’t engage in any gear at all. This is because of a failing torque converter, broken oil pump pinion, lack of lubrication in the system, clogged filter, worn friction clutches, broken collar, and jammed valve.
  • The car engages in R and in the first and second gear. The valve in the hydroblock is jammed.
  • The transmission “slips” when the car starts to move. This is due to worn-out clutches.
  • When driving, the shifter is in the “D” position, but the car refuses to move when the accelerator pedal is pressed. In this case, the driver switches the automatic transmission to manual mode (if available), and the gears work well.
  • The automatic transmission does not shift higher than the third gear.

When these failures in the operation of the automatic transmission occur, the car’s Electronic Control Unit (ECU) will put the AT in emergency mode. If the owner is faced with one of the problems described above, first of all, it is necessary to carry out computer diagnostics using an OBD to see the exact faults.

How to fix an automatic car that does not shift gears

Based on the symptoms above, you should check the following:

1. The level and condition of the transmission fluid.

The level should always be normal, and the same goes for the condition. If there is not enough oil in the system, the cause of the leak must be identified and solved.

If the quality of the fluid is poor, mostly due to the presence of dust from friction disc wear, then the discs should be replaced and the lubricant changed. Do not forget to flush the system several times.

2. Friction Clutch Condition

Friction clutch wear is one of the most common problems regarding the inability of the transmission to shift. Diagnose and, if necessary, replace the friction clutches.

3. Other transmission parts

Check the valves for proper operation. If they are jamming for any reason, they should be changed. Check the functionality of the rocker and the electrical wiring of the transmission system

How to avoid problems with automatic transmission in the future

  • Use the neutral gear only if you need to. The “N” is considered a service mode, so limit its use.
  • Warm up the automatic transmission in winter. If the AT is not heated enough, the probability of failure for certain parts is high.
  • Cars with automatic transmission should not tow anyone, since these are simply not adapted to this. Loads have a very negative effect on the unit. If you are planning to drive with a trailer, then consider this factor when buying a car.
  • Don’t try to push-start an automatic car.
  • Try not to tow an automatic car with a cable. When the engine is turned off, the fluid will not lubricate the system, and this will negatively affect the transmission as a whole. Use a towing truck instead.
  • Always use only high-quality transmission fluid recommended by your car manufacturer. Using a cheaper lubricant over time can only do more harm than good.
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