The mechatronic unit is the heart and soul of the gearbox in a DSG Gearbox (direct-shift gear oil). The job of mechatronics is to manage the clutch pad and the torque converter. It does this by transferring fluid under specific pressure. This ensures shift operations happen within a second. Between the gearbox and the engine is constant collaboration because gear shifting has to happen perfectly between both components.

The mechatronic unit is usually found in vehicle with a duel-clutch transmission. In other words, two sub-gearboxes that each function with their own clutch. The unit consists of valves and sensors so that clutches are opened and closed in absolute precision.

The components of the mechatronic unit are the control unit, the valve body and the solenoids.

The Control Unit

The control unit collects and analyses data regarding the mechatronic system. Component needed to conduct such an analysis are the speed, temperature, and pressure sensors. The unit makes use of the information to execute the programs for gear-shifting. As a side bonus it also checks for malfunctions that can often appear.

The Valve Body

This component takes up the job of hydraulic control in an automatic transmission. The valve body manages the flow of fluid between the torque converter and different parts of the gearbox. Components of the valve body are the following:


Hydraulic valves

Plastic and metal balls

Manual valves

Plates with fluid pad and valve seat


These are electrohydraulic valves. They are the executive elements of the control unit inside the mechatronic. So basically, they run the operation. The manage the hydraulic valves found in the valve body. The solenoids allow the transmission fluid to flow under the necessary pressure and they can also work on high frequencies therefore gear-shift happens quicker.

Problems with The Mechatronic Unit

The most common problems happen when any of the above-mentioned components are not working as they should. This is the most obvious error. Also, sensor can also malfunction and when that happens data collection can’t happen. And since data cannot be properly collected the gearbox sends through many error messages. The software programme of the gear control will appear in error due to this.

Most often the error starts with faulty sensors. An example is the temperature sensor. If this sensor stops working then the data it receives is incorrect and then the mind behind the computer will attempt to do the right thing off incorrect data and thus failure ensues. This causes gears to stop working or in part stop working.

The valve body undergoes its own set op problem and most known is appearance of gaps between valve seat and normal wear-and-ear of a valve. When certain elements that are not part of transmission fluid then valves rapidly deteriorate.

Most failures also only transpire due to general problems in automatic transmission.

Get proper diagnostics! This is crucial!

Common Faults with Mechatronics

Clonking in gears

Warning lights

Inability to select gears

Gearbox keeps selecting “NEUTRAL”

“PRNDS” Lights are on

Troubleshooting a Mechatronic Unit

As you can assume this is a complex task. You will have to be educated on the codes for trouble shooting. Repairs can become very expensive and it’s important to know how to identify malfunction in your mechatronic unit. Many units all look the same but they are completely different and have very different hardware and software operating systems and replacing the unit can cause so many driving problems. It can also lead to issues with the car like for example clutch wear-and-tear, inability to function for the mechatronic unit, etc.

If your “PRNDS” Lights are flashing then your gears will mostly just remain in neutral and/or have the inability to shift. As we all know small issues lead to big problems.

If you feel there is a fault in your mechatronic, your first stop is a qualified workshop you trust! They can make a diagnosis and you can budget for repairs.

Electrical defects will call for a complete disassembly of the unit so it can be completely inspected and when the malfunction is found then the repair can happen. They will inspect solenoids, sensors or mainboard electronics.

Mechanical defects will apply the same process of disassembly, but they will inspect mechanical faults like the torque converter, valve body and the gearbox.

The valve body is usually in itself dismantled and inspected. They will also need to check of there is freeze in the transmission fluid.

Inside the valve body is oil passages and these passages are inspected for any out of place particles. Once that’s done the valve body is cleaned up. If even after that the particles are still stuck then that is an indication of serious mechanical problems.

Wear-and-tear are also a big headache, but to do determine if that is what’s causing the malfunction then two tests care carried out. The test is conducted on a high-tech stand and specifically tests the pressure and temperature of the valve in real conditions and then there is notice of error or the absence of the error. The other test is manually conducted with a valve machine testing each valve.

The mechatronic unit is very sensitive and needs competent specialists assisting in its repair. Luckily VAG Spec centre Zeerust can repair mechatronic units. We are a 5-star, RMI-approved workshop and we have handled many mechatronic units and repaired them. Trust the specialists!


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