Why automatic transmission slows down and how to fix it

Automatic transmission slipping: causes

The average service life of automatic transmissions is 250 000 km. However, automatic transmission slipping can significantly reduce this period, so you need to eliminate the problem at an early stage.

Symptoms of automatic transmission slipping

About the stall can be said if during the movement the engine begins to run at idle speed during the shift to a higher gear. If you do not pay attention to this, the problem will worsen and the car will start slipping more often. After a while the slipping will occur already during starting and when shifting to higher and lower gears. It looks as if the engine strongly increases its revolutions, but at the same time the speed mode does not change.

When slipping, jerks are also possible, the engine starts to work jerkily. Other signs of this unpleasant phenomenon – deterioration of acceleration dynamics and poor response of the car to pressing the speed pedal.

When slipping, you may observe increased revolutions – it is about the discrepancy of revolutions to the speed mode. For example, you have established that at 120 km/h you have 3 000 revolutions. But one day you notice that at the same speed, the tachometer shows about 4,000 rpm. And all this while driving on a flat road and with an unloaded car. In especially severe cases, slipping is accompanied by noise, knocking and other unpleasant sounds. Vibration may appear.

Automatic transmission stalling: causes

When the automatic transmission slams, you need to check the transmission oil. Pay attention to its level – it must correspond to the norm. If necessary, it is necessary to replace the oil or refill it.

Sometimes there are more serious problems:

  1. Destruction of friction, which are clutch elements (slippage begins when the engine is cold).
  2. Failed solenoids (this problem occurs “when the engine is hot”).
  3. Hydraulic system is out of order (this is the consequence of contamination of oil pump channels).
  4. Failure of air filter (the problem appears when starting the engine).

Below we will tell you what the driver should do with different symptoms of slipping.

On hot.

If the oil has been replaced, but the problem with stalling remains and the automatic transmission sticks on hot, this is an evidence of a failure of the solenoid block. The solenoids are deteriorating due to the use of low-quality fluid. You will have to replace the electromechanical valves, because the lifetime of the solenoids is less than the lifetime of the transmission. Before replacing electromagnetic valves it is worth to measure pressure in the transmission system – it will help to reveal the reason of gearbox failure.

If the pressure is low (this is when slipping of fractional gears “on hot” occurs), it is possible to say that the problem is in the solenoids or in the oil pump. After replacing the faulty nodes, the work of the automatic transmission is fully restored.

Often in this case it is necessary to change the valves – it is better to do it in batches of solenoids, as a single replacement may not give results.

On cold

If slipping occurs “when cold”, it is necessary to check the friction discs installed on the planetary gearbox. The friction clutches work in a hard mode, so they wear out rather quickly. The rated life of the friction clutches is 250,000 to 300,000 km of mileage. This is about the same as the entire automatic transmission, but the friction clutches can break down long before the car covers the proper distance.

On off-roading.

Stalling occurs when the accelerator pedal is depressed sharply. At the same time, you can hear the sounds of rubbing elements that cannot “grip”. The clutch appears after a slight depressing of the accelerator pedal. But if you do not release the gas, you can hear a strong shock in the area of the automatic transmission. Usually such problems appear in the first gear.

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Such malfunction can be observed not every time. For example, after leaving the garage there were extraneous sounds in the area of “automatic transmission”, and during the second start of the engine there are no sounds anymore.

With a special device we determine the frequency of revolutions of the automatic transmission primary shaft – if it corresponds to the revolutions of the engine crankshaft, the problem is in stalling from the spot. Zero value speaks about malfunction of torque converter. Anyway, automatic transmission should be repaired.

In all gears

While shifting from one gear to any other gear, an overdrive begins to occur. This is similar to how it would be if in a manual transmission, press the clutch without reducing the revs. The next gear is then, of course, engaged, but only after a pause. If you sharply press the accelerator pedal, you can expect a strong jolt. Slipping occurs exactly at the moment of gear shifting – at other time the engine operates as usual.

It can occur because of heavy overloads, when the usual speed mode of driving is not less than 150 km per hour. The oil burns quickly, and the friction clutches themselves burn after it. Here there is a clear need for repair of the gearbox with the obligatory replacement of the filter.

When shifting from 2nd to 3rd gear.

This problem can be solved by replacing the brake band. You will have to dismantle the side cover and check it for wear of the seals.

Automatic transmission stalling: what to do?

It is necessary to carry out a diagnosis of the automatic transmission. Sometimes the cause of stalling is a malfunction of the electronic control unit. Electronics begins to send incorrect signals to the mechanics – this is the cause of the problem. In this case, it is better to replace the ECU completely. The malfunction is detected by computer diagnostics.

How to conduct diagnostics

Slipping of the automatic transmission can be determined by noises and incorrect behavior of the machine when shifting gear modes. Making diagnostics of automatic transmission in a garage is not recommended – here the help of professionals is needed.

The most common way to identify malfunctions – computer diagnostics. By the way, it is the most accurate and allows for a short time to localize the malfunction on the basis of the error codes issued by the system.

Automatic transmission repair is a complicated thing, in most cases it requires disassembly of the unit. Only after that the preliminary diagnosis given out by the electronics can be confirmed or refuted.

If the automatic transmission slips, it is a serious problem, which should be solved by professionals. In case of automatic transmission slipping, it is necessary to go to a service station to carry out professional diagnostics of the unit. The automatic transmission is controlled by electronics, therefore standard diagnostic methods are unlikely to be effective – it is necessary to have the software and special equipment at hand. Sometimes the problem is solved by replacing the oil filter, but in most cases the unit must be disassembled completely.

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Automatic transmission sticks: the main symptoms and causes

Automatic transmission – a complex, but quite reliable unit, the average service life of which exceeds 200 thousand kilometers of mileage.

Automatic gearbox stalls

But in case of an automatic transmission failure, be prepared to shell out a decent sum of money. Preventing such troubles is a much easier task than fixing them. Today we will talk about automatic transmission slipping – a problem that can threaten very serious trouble for the car owner.

It is important not only to know the main manifestations of this malfunction, but also to understand the causes of their occurrence – this will help to make a quality diagnosis of the transmission, which will prevent its complete failure.

Symptoms of automatic transmission slipping

If 15-20 years ago the automatic transmission was installed only on the top models of medium and luxury cars, then today the automatic transmission is no longer a sign of prestige. They equip with them both SUVs and miniature city cars. This type of transmission is especially loved by female part of driver’s community.

The main factor of such popularity is obvious – the ease of driving the vehicle. However, due to different reasons, with time the ease of gear shifting loses. One manifestation of this problem is slipping – a phenomenon that not only reduces the efficiency of the transmission, but which can lead to more serious and unpredictable consequences.

It is well known that the main task of a gearbox, including automatic transmissions, is to transmit torque from the power unit to the wheels, preferably without any tangible loss of power. An automatic transmission is good because it carries out the set tasks practically without the participation of the driver. Of course, it is achieved due to the complication of the design. The more complex is the device, the higher is the probability that one of its numerous components will fail. This thesis is also true for the automatic transmission. One of the most characteristic problems, which tell about the beginning of the appearance of troubles – slipping when shifting gears.

That is why it is so important to be able to recognize the symptoms of slipping gears of the box in the early stages. Let’s list them:

  • A sharp increase in the number of revolutions of the power unit. Usually it happens with automatic transmission slipping – to shift from 3rd to 4th gear it is required to increase revolutions to the level of about 3-3.5 thousand, and only after that the shift itself happens (that is we have an imitation of Overdrive mode).
  • Longer car coasting motion. If you have noticed that after taking your foot off the accelerator pedal, the car for some time continues to move as if on inertia, without engine braking – it is also one of signs of automatic transmission slipping.
  • Longer shift to lower gear. It is highly probable that longer shift, for example, from second to first gear is caused by automatic transmission slipping. In some cases, the engine revs up before the automatic transmission engages a downshift. So a delay in shifting gears is another symptom that the automatic transmission is slipping.
  • Another classic sign of such malfunction should be considered a delay in the acceleration of the car when pressing the accelerator pedal. Sometimes such delay is accompanied by a decline in engine power.
  • One can also understand that the automatic transmission is stuck by the color of the transmission oil. Normally, this liquid has a distinctive reddish tint, but when the gears slip, their destruction occurs. As a result, the smallest metal particles in the oil, oxidizing, give it a brownish tint.
  • The appearance of uncharacteristic sounds in the form of grinding when driving at high speed should also alert you. In the initial stages, grinding is heard mainly during acceleration and braking in high gears, but over time, the noise appears with enviable regularity, and its duration increases. In such cases it is highly recommended not to hesitate to diagnose the transmission.
  • If you began to experience problems when shifting into reverse gear, most likely it is the automatic transmission that is slipping. The manifestation of this symptom is especially characteristic in cold weather, at subzero temperatures. As a rule, inclusion of reverse is accompanied by a time delay and does not happen as smoothly as usual.
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It is not necessary to remind, that if any of the listed symptoms occur, it is necessary to think over, and if they appear in plural quantity and simultaneously – it is better not to exploit the car until the reasons of slipping and their elimination are defined.

Symptoms of automatic transmission slipping

Diagnostics of automatic transmission

The initial diagnosis is just to identify the symptoms that indicate slipping of the transmission. As a rule, it is possible to determine that the automatic transmission is stuck, and independently on the basis of the appearance of various noises and unusual behavior of the car when shifting gears. Based on the detected symptoms, you should contact a specialist, as an independent clarification of the diagnosis will require disassembly of the box. If with a manual gearbox it is quite acceptable even in garage conditions, with an automatic – no.

The simplest and exact enough way to reveal malfunctions is a computer diagnostics, which allows localizing a malfunction in some minutes on the basis of received error codes.

In the vast majority of cases, repair will still require disassembly of automatic transmission, and it is at this stage that the preliminary diagnosis obtained on the basis of computer diagnostics is usually confirmed or refuted. Of course, this work should be performed by qualified specialists. Without appropriate experience and skills, attempts of self-repair are doomed to failure in 99% of cases. So slipping of friction clutches is not an insignificant problem at all.

Causes of automatic transmission slipping

Like most other malfunctions, automatic transmission gear slipping begins subtly. However, it is also possible to detect this problem early on. For example, you can tell by overly reluctant acceleration with a recessed accelerator pedal. As soon as you have suspected something wrong – immediately address to the nearest auto service center for carrying out of diagnostic actions. This will allow you not only to reveal the cause of slipping in time, but also to prevent considerable expenses in case of complete failure of automatic transmission.

Most of the causes, due to which the automatic transmission stalls, are the result of improper use of the automatic transmission. Let’s list the most typical of them:

  • Falling TM level (this should be monitored not with the same regularity as the level of engine oil, but many car owners ignore this obligation at all);
  • significant deterioration of transmission fluid quality, which will be evidenced by a change of oil color to dark, detection of mechanical inclusions in it (dust, chips, particles), thickening of the TM, the smell of oil sticking)
  • the friction clutches have started to deteriorate – in such cases the slipping occurs when the engine is cold
  • Faulty electromechanical valves of the transmission (solenoids) – this is the cause of slipping of automatic transmission in hot conditions;
  • Hydraulic system malfunctions caused by contamination of the hydraulic unit oil channels or the oil pump itself;
  • significant deterioration of the air filter is manifested by the occurrence of slippage at the beginning of machine movement;
  • errors in operation of automatic transmission control unit, which usually appear at transition of a selector from one mode to another.
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Let’s consider some of these causes in more detail.


The hydraulic system is an important component of the automatic transmission, and it is often the main reason why the automatic transmission stalls. As a rule, most of the problems are caused by clogged hydroblock channels. This leads to the violation of the normal process of transmission components lubrication, which leads to slipping of the friction. There is also a solution to the problem – quality cleaning of oil ducts, as well as air filter replacement at the same time. The preferred way to perform such works – in a car service, equipped with the appropriate specialized equipment. Recently, however, alternative ways of hydraulic system treatment have also become popular. For example, using special cleaning compositions or by means of ultrasound. In a word, nowadays the specialists have at their disposal quite effective technologies, which allow getting rid of any contamination of hydroblock channels. But in any case the given action is performed with disassembly of hydraulic system, and it is a rather labor-intensive operation, which will take at least two days.

As a rule, if the hydraulic pump or channels are dirty, the automatic transmission stalls when the car accelerates.

Solenoid Block

The previous malfunction, as already noted, requires a large amount of repair work, with complete disassembly of the hydrogroup. Usually, after such an operation, all the filters are also replaced. Of course, transmission oil is also changed. But that is not all: if slipping of the automatic transmission in hot conditions occurs as a symptom, electromechanical valves are changed at the same time, since solenoids are not consumable but their resource is usually lower than the service life of the box itself. Especially they wear out quickly, if you use transmission oil of unknown quality. Measuring the pressure level in the transmission lubrication system is an operation, usually preceding the replacement of electromechanical valves. It allows you to identify all the nuances concerning the wear and breakage of solenoids, as well as other problems in the automatic transmission.

If it turns out that the pressure is lower than the nominal one (this is the cases when slippage of friction gears is observed on heated up power unit), then it is possible to assert with confidence that this is the result of failure of solenoids or oil pump. If you have figured out why your automatic transmission is stuck, just replace all the faulty parts. If the work is done on a high professional level – you can rest assured that the performance of automatic transmission will be fully restored.

One last good tip – when replacing valves, do it in batches of solenoids, not one at a time. You’ll spend a little more, but you’ll be sure to reduce the likelihood of the same failure by an order of magnitude. By doing so, you’ll extend the life of an expensive gearbox.

Friction clutches

If it has come to disassembly of automatic transmission, you should not refuse to perform diagnostic procedures for friction clutches, because they can also be the cause of slipping of automatic transmission, but on a cold engine. The matter is that friction clutches have to work in very rigid conditions, and therefore wear out as quickly, as solenoids. It is diagnosed by instrumental methods, and the nominal value for the friction clutches is about 240,000-300,000 kilometers of run. In principle, it’s comparable to the service life of the complete transmission, but the onset of friction failure may occur long before the allotted mileage has been reached. Note that replacement of friction clutches also refers to the works of increased complexity, so you can not even think about self-repair.

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Reasons of automatic transmission slipping

Automatic transmission ECU

If the elimination of all the above causes has not solved the problem, you can only sin on the malfunction of the controlling electronic unit. The malfunction of the ECU of the transmission, it turns out, can also affect the work of separate elements of the gearbox. What to do if automatic transmission is stuck exactly because of malfunctioning electronic unit? There are cases when the problem is solved by firmware update, but more often the ECU has to be replaced with a new block. It is easy to diagnose such malfunction with an onboard computer, but both diagnostics and ECU replacement is a procedure that requires appropriate knowledge and equipment, so you can’t do it with your own hands. Get ready that the cost of this operation specifically for your automatic transmission will not coincide with the market average. This is quite acceptable, since it depends on the design of the box, and it is different for all major manufacturers.

As we can see, independent repair of automatic transmission is not recommended, even if at first glance it seems that no difficulties should arise. If manual transmissions are arranged similarly in principle, the differences are mainly in geometry, with automatic transmissions the case is completely different. The slightest mistake during installation – and the chance to finally break the automatic transmission will increase rapidly, and it is one of the most expensive (after the engine) nodes of a modern car.

Brief results.

So, if we found out that the deviations in the behavior of the car are associated with the slipping of the automatic transmission, you should immediately go to a proven service station to perform diagnostics of your box.

It is the diagnosis that allows you to clarify the diagnosis and begin troubleshooting, knowing exactly what will have to be replaced. Since the work of automatic box is controlled by its own electronic unit, you can not perform diagnosis with standard means – you need to have the appropriate equipment and software.

Sometimes this procedure does not reveal the problems, and after replacing the TM and oil filter, transmission operation becomes normal. But if there are symptoms of pinion wear, in most cases you have to solve the problem by carrying out a complete disassembly of the unit. In particular, it can’t be avoided in case of a faulty hydroblock or broken friction rings.

Automatic transmission ECU

It is impossible to estimate repair budget in advance, since everything depends on a particular fault, and there may be several of them during repair of the box.

Don’t be surprised if it turns out that even the transmission oil change operation will cost much more than the oil change in the power unit – the complexity of this operation is corresponding, which has a decisive influence on the price formation.

Appearance of slipping symptoms means that problems are already there, and repair most likely cannot be avoided. But if you exactly follow the automaker’s recommendations concerning the use and servicing of automatic transmission, you can be sure that the box will serve you for at least the declared terms. That means you will manage to avoid expensive repair, which is unreal to do by your own forces.

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