Automatic Transmission Control Unit: Where is the ECU Located, Electronic Switching, Diagram, How to Find Malfunctions and Breakdowns, Diagnostics, Repair Details

The information collected by the sensors about the operating mode of the transmission is transmitted to the ECU. There, information is processed and the subsequent creation of corresponding control signals. To improve the operation of the automatic transmission, the algorithms embedded in the control unit are constantly becoming more complex. Now the gearboxes are able to adapt to a sporty driving style or to driving on an icy road.

ECU appearance

Types of automatic transmission electronic control units

There are two main types of electronic control units:

Separately responsible for the operation of the automatic transmission. In this case, the device is assigned to control only the gearbox. The advantage is the lower price compared to combined blocks. It can be placed externally, for example, in the car interior or engine compartment, or be built inside the automatic transmission housing;
Combined with engine ECU. Designed to reduce vehicle components and take into account the interaction of the engine and gearbox. All information is processed by a common processor, simultaneously issuing commands to the engine and gearbox. The result is more optimized operation of the power plant, since more external factors are taken into account when generating control signals.

When manufacturing an ECU together, it is almost impossible to use the placement of the device inside the gearbox, so the number of cables going to the control unit increases. This, in turn, does not have the best effect on the reliability of the system. The wires in the cable have a thin cross-section, which causes frequent damage.

Problems that may arise when repairing the electronic transmission control unit

When repairing an automatic transmission ECU, certain difficulties may arise:

The first and, unfortunately, the most common problem is the unavailability of the necessary parts and microcircuits for the ECU. This may happen if you have a car equipped with an automatic transmission, which is not popular in our country. In this case, spare parts will have to be ordered from the country of the car manufacturer. Not only will you have to wait a very long time for them to arrive, but the cost for them will be many times higher than for similar spare parts for popular models. In addition, if the car brand is outdated, it will be almost impossible to find spare parts via the Internet.
The second important problem is that it is not possible to repair the transmission ECU in every city due to the lack of experienced technicians. It often happens that a car service center has all the necessary equipment, but the master can at most remove errors from the ECU memory.
It often happens that the problem with the operation of the ECU is micro-breaks in the wires. Because of this, information does not constantly enter the processor. As a result, errors occur that interfere with the correct operation of the automatic transmission. As a rule, when conducting diagnostics, the technician sees the error itself, which he deletes, but does not notice the very essence of the problem. Having eliminated the error, he considers that the work was done efficiently. But after some time the problem arises again. Finding a microtear (fault) is very problematic. This takes a huge amount of effort and time. And in the case of a car owner - also money.

If you have a problem with the electronic transmission control unit, to solve it you need to contact large specialized car services that provide a guarantee for all the work they carry out. If the service does not issue a guarantee for repairs, you may encounter the problem that comes third in the list above.

Types of automatic transmission electronic control units

There are two main types of electronic control units:

Separately responsible for the operation of the automatic transmission. In this case, the device is assigned to control only the gearbox. The advantage is the lower price compared to combined blocks. It can be placed externally, for example, in the car interior or engine compartment, or be built inside the automatic transmission housing;
Combined with engine ECU. Designed to reduce vehicle components and take into account the interaction of the engine and gearbox. All information is processed by a common processor, simultaneously issuing commands to the engine and gearbox. The result is more optimized operation of the power plant, since more external factors are taken into account when generating control signals.

External placement

In this case, the block is manufactured in a closed housing. It can be either a separate element or combined with the engine ECU. There are different locations of the module, for example, in the dashboard or engine compartment. An example of the brains of an automatic transmission is shown in the figure below.

External location in a closed housing

There are a large number of sensors inside the transmission. When the control module is moved outside the box body, it becomes necessary to lay a large number of wires. At the same time, it is important that the automatic transmission housing remains sealed and transmission fluid does not leak out.

The advantage of this solution is the ability to place the ECU anywhere. This protects electronics from exposure to high temperatures and aggressive environments. Finding a breakdown and making repairs is also easier when placed externally.

External placement

External location in a closed housing

There are a large number of sensors inside the transmission. When the control module is moved outside the box body, it becomes necessary to lay a large number of wires. At the same time, it is important that the automatic transmission housing remains sealed and transmission fluid does not leak out.

Internal layout

When placed internally, finding where the automatic transmission control unit is located is not difficult, since the ECU is located inside the automatic transmission. The length of the wires is kept to a minimum. All of them are located inside the case. The appearance of the electronic unit, designed to be placed inside the transmission, is shown below.

Internal execution

The main disadvantage of this arrangement is the constant exposure of the electronics to high temperatures. Repairing the automatic transmission ECU also becomes more complicated. To inspect the module, the gearbox will need to be disassembled. This greatly complicates the troubleshooting of the module and, accordingly, increases the cost of repair work. Automakers have not yet found a compromise solution between external and internal placement.

Control unit design

Standard elements of the control system are:

Permanent memory that stores the operating algorithm. With chip tuning, it is possible to make changes to it. During normal operation of the car, the memory data remains unchanged;
RAM. It processes all data received from sensors in real time;
A processor that executes a specific set of instructions. Very often it has a chip combined with memory;
Galvanic isolation. Prevents module damage from incorrect sensor operation. They also serve to protect against incorrect connection of measured signals.

Each automaker produces an electronic automatic transmission control unit with its own filling. The number of chips on the board is growing, despite the fact that the functions of individual elements are being combined. This is due to the complication of the algorithms being executed and the increase in the amount of information received from sensors. The circuit loses its maintainability, so often when the ECU fails, it is recommended to replace it with a new device.

Internals of the automatic transmission ECU

Reasons for failure of the automatic transmission ECU

In most cases, malfunctions of the automatic transmission control unit lead to complete immobilization of the car. In some cases, gear shifting occurs incorrectly, or the gearbox can only operate in emergency mode. The cause of breakdowns of the automatic transmission control unit can be:

onboard voltage surges. especially in the direction of exceeding the nominal value;
mechanical damage due to impact;
parasitic vibration that appeared due to a malfunction of any vehicle system, for example, the brake system;
excess operating temperature;
factory defects in both software and module circuitry, which is especially important for domestic cars;
influence of an aggressive external environment.

Damage to the electronic control unit board

The reason why control information is not processed may be burnout of any element on the board. Depending on the damaged element, a method for solving the problem is selected. For example, the capacitor can be replaced with a new one. Resoldering a processor is a labor-intensive process, so when it burns out, the board is replaced with a new one.

TCM, CVT, DSG modules – automatic transmission control

Modern automatic transmission on-board computers operate in constant mode, analyzing information received from sensors every second and reacting by sending commands to the transmission actuators. The system is involved in almost all components of the car, and its brain center is the electronic transmission control unit .
Like any microcircuit, the automatic transmission ECU can also fail and require repair. What causes failure of the automatic transmission electronic unit?

Mechanical impact: overheating, power surge, corrosion, “flooding” of the unit with technical fluids, constant vibration, shock during an accident;
Software errors: Certain car models have "chronic" transmission computer problems. These faults can appear throughout the entire period of use of the car;
Incorrect operation of the automatic transmission - frequent departures from the transmission characteristics declared by the manufacturer provoke increased wear of the circuit board;

If the gearbox starts operating exclusively in third gear mode without the possibility of changing the position, with 95% probability it can be said that a failure that cannot be corrected by standard means has occurred and the automatic transmission has switched to an “emergency” operating mode, allowing you to get to the nearest service station.

This usually happens when the electronic transmission control module stops receiving input from a sensor or loses communication with the slave solenoid. In this case, it is recommended to immediately diagnose and repair the transmission ECU and related systems. If there is no suitable service station nearby, it is better to call special equipment to transport the car.

We repair any electronic transmission units ourselves in our own equipped laboratory, which eliminates the markup of intermediaries and increased repair time.
High-quality repairs will extend the life of the automatic transmission ECU for years.

Diagnostics of the electronic control unit

Several methods are used to identify the culprit of the malfunction:

Electronic diagnostics. The ECU is connected to a personal computer or laptop to read the error log. In addition to searching for a breakdown, during the procedure it is possible to optimize the program so that the automatic transmission control is adjusted to the owner’s wishes. When diagnosing, it is recommended to reset random errors so that the electronic control unit continues to operate normally;
Advanced diagnostics. It is carried out in the event of incorrect electronic diagnostics that are unable to detect a breakdown of the gearbox ECU. The reason for using an extended check may be a break inside the module that prevents reading error information;
If it is impossible to determine the failed element using the previous methods, they resort to one by one replacing individual parts of the ECU, the breakdown of which is most likely. This method is extremely rarely used on serial automatic transmissions, since it is more economical to purchase a new control board.

Diagnostics of the electronic control unit using a laptop

Before starting diagnostics of the electronic control unit, it is recommended to check the condition of the cables going from the automatic transmission to the computer. It is also worth making sure that the sensors are working and that there are no oxide deposits on the contacts. Failure of meters is much more common than failure of the control module.

Automatic transmission ECU repair prices

Prices for ECU and automatic transmission repairs may differ from the cost of work in your city, but not significantly, since this article contains average values from several cities in Russia, including Moscow.

Electronic diagnostics – 1500 rubles. It is carried out using a computer with a special program. With such diagnostics, the operation of the ECU is optimized and all errors that prevent the control unit from functioning normally are removed.
Advanced diagnostics. Advanced diagnostics should be carried out if electronic diagnostics are not possible for any reason. Most often, it is necessary due to breaks in the line or failure of the automatic transmission ECU processor. The cost varies from 1500 to 3000 rubles.
Replacement of individual ECU blocks. Only a master can determine the exact cost. For each specific case it is determined separately. Its components are: the cost of the necessary parts and the complexity of the work.

Control unit under repair

Subtleties of automatic transmission ECU repair

Chips for repair are available only for mass-produced cars of recent years. For other cars, components must be ordered from the automaker, which significantly increases the cost compared to popular models. The interchangeability of the ECU is low, so even within the same brand of car there may be several versions of the module, for example, with differences in pinout.

When performing diagnostics, much depends not only on the availability of the correct software, but also on the experience of the technician in decoding the error log. Self-diagnosis is not able to accurately indicate a breakdown, so relying only on scanner readings can waste money. Many technicians only know how to remove an error from memory, which will return after a short period of time.

Microdamage to conductors makes it difficult to determine a fault. The signal from the sensors does not arrive all the time. So, when carrying out diagnostics, all information enters the ECU in full, but it is enough to drive out onto the road and the data flow is interrupted. The electronic module records the error and puts the gearbox into emergency mode. For the same reason, the control signal may also be lost.

The automatic transmission electronic control unit is small in size, but it can damage the transmission, therefore, at the slightest suspicion of a malfunction of the ECU, it is advisable to diagnose the module. It is prohibited to drive a car with a malfunctioning unit, as this may lead to loss of control of the car while driving. It is difficult to repair electronics yourself, so it is recommended to turn to professionals if necessary.

If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them

How to repair an automatic transmission ECU

To ensure the proper level of quality when repairing an automatic transmission ECU, our employees carry out diagnostics of the device accepted for service - the information obtained about the condition of the control unit in the future will make it possible to most effectively plan repair work.

According to our statistics, in 80% of cases, ECU repair is not required, because... The problem most often lies in the car's wiring.

After this, the faulty ECU is removed from the car, and the failed elements are replaced. After assembly, the control unit is installed back, connected and checked for correct operation. Testing can be carried out on a special stand or directly during a test run of the automatic transmission. After successful re-diagnosis, the car is handed over to the owner.

To make an appointment for ECU repair, leave a request on the website or call +7 (495) 532-41-61.