Why Has My DSG Gearbox Lost Half Its Gears?

DSG and S tronic gearbox faults: what happens when you suddenly lose a group of gears?

There are few things more alarming than driving your Volkswagen, Audi, Škoda or SEAT and suddenly finding that your gearbox has stopped behaving normally.

Perhaps the car will only select certain gears. Maybe you have suddenly lost 1st, 3rd, 5th and 7th gear. Or perhaps it is the opposite and the car is only offering 2nd, 4th and 6th. You may also notice the engine revving unexpectedly, the car hesitating between gears, or a gearbox warning appearing on the dashboard.

The first thought is often the same:

“The gearbox has failed. How much is this going to cost me?”

The good news is that losing a group of gears does not automatically mean the complete gearbox needs replacing.

With modern DSG and S tronic transmissions, the symptoms and fault codes can provide valuable clues about where the problem lies. However, those clues still need to be properly diagnosed rather than simply used as a reason to start replacing expensive components.

At Boam Automotive, we regularly work on Volkswagen Group vehicles and understand how important it is to establish the cause of a transmission fault before deciding on a repair.

Why can a DSG gearbox lose a group of gears?

A DSG transmission uses two clutches and a mechatronic control system to manage gear selection and clutch operation.

In simple terms, the gearbox is designed so that different groups of gears are controlled through the two sides of the dual-clutch system. This is why a fault affecting one side of the system can sometimes result in a very distinctive pattern of lost gears.

For example, a fault can result in a vehicle being left with:

1st, 3rd, 5th and 7th gears

or:

2nd, 4th and 6th gears

The exact behaviour depends on the transmission and the fault involved, so this pattern should be treated as a diagnostic clue rather than a diagnosis in itself.

The important point is that the gearbox may still be mechanically capable of selecting some gears while another part of the transmission control system is preventing the others from operating correctly.

What is the DSG mechatronic unit?

The mechatronic unit is a crucial part of a modern DSG transmission.

It combines electronic control and hydraulic functions to control the gearbox, including the operation of the clutches and the selection of gears. It receives information from various sensors and uses that information to determine how the transmission should operate.

This is why a fault within the mechatronic system can produce some very unusual gearbox symptoms.

A vehicle may appear to have a serious mechanical gearbox failure when the underlying problem is actually within the transmission’s control system.

That is also why reading the fault codes is only the beginning of the diagnosis.

What do DSG position sensor fault codes mean?

One example we see on VAG transmissions is a fault relating to clutch position sensing.

The transmission needs to know where the clutch is positioned so that it can accurately control clutch engagement. If the position being reported by the sensor is outside the expected range, the transmission can detect a fault and may enter a protective or limp-home strategy.

For certain Audi applications, manufacturer technical information specifically documents cases where vehicles can lose either the odd-numbered or even-numbered gears alongside clutch position-sensor faults. That provides a good example of why the combination of fault codes, symptoms and live data can be so important when diagnosing a DSG or S tronic transmission.

However, seeing a particular fault code does not automatically mean that the corresponding part should simply be replaced.

A fault code isn’t the same thing as a diagnosis

This is one of the most important things to understand when dealing with modern vehicle diagnostics.

A diagnostic scan can tell you that the vehicle has detected something outside its expected parameters.

It does not always tell you, by itself, which component should be replaced.

A good diagnostic process looks at the bigger picture:

• What is the customer experiencing?
• What fault codes are present?
• What was the vehicle doing when the fault occurred?
• What do the relevant sensor values and pressures show?
• Can the problem be reproduced?
• Does the evidence point towards the clutch, mechatronic system, wiring, sensors or another cause?

Only after those questions have been answered can an informed decision be made about the repair.

A real DSG fault diagnosed in our workshop

We recently dealt with a vehicle where the diagnostic information provided a particularly useful example of this.

A diagnostic scan was carried out and the clutch position sensors were assessed using suitable diagnostic equipment. The data showed that clutch position sensor 1 was outside the specified range.

More importantly, when the fault occurred, the corresponding clutch pressure reading was showing -1 bar.

Taken together, those readings indicated an internal fault within the mechatronic unit rather than simply giving us a generic “gearbox fault”.

The mechatronic unit was removed in accordance with the relevant manufacturer repair procedures and replaced. The gearbox was then refilled with the correct fluid, the required basic settings and mechatronic adaptation procedures were completed using diagnostic equipment, and the vehicle was tested afterwards.

Following the repair and testing, no faults were present at the time of the final check.

The important part of the job was not simply replacing the mechatronic unit.

It was proving that the mechatronic unit was the cause of the problem before replacing it.

Another example: when a suspected clutch problem wasn’t the end of the story

We also recently had a Volkswagen Golf booked in after the customer reported that the car was over-revving, particularly downhill, and sometimes appeared reluctant to change gear.

A clutch-related repair was initially being considered.

Rather than simply fitting the clutch pack, the vehicle was investigated further.

A full fault-code scan identified a gearbox fault relating to clutch clearance. We then carried out multiple test drives, both hot and cold, to reproduce the customer’s complaint and better understand how the transmission was behaving.

Further work was then carried out on the transmission mechatronic system. The unit was removed, inspected and cleaned, including removal of debris from the magnets, before being refitted and the gearbox basic settings being carried out.

Following the work, the vehicle underwent an extended road test and the gearbox control unit was scanned again.

No gearbox fault codes were present at the time of the final test.

This is a good example of why we believe diagnosis should come before parts replacement.

A gearbox problem can produce symptoms that make a particular component look like the obvious culprit. Sometimes it is. Sometimes further investigation tells a different story.

Does a DSG fault mean I need a new gearbox?

Not necessarily.

A DSG or S tronic transmission is made up of a number of different components and systems, and a fault in one area does not automatically mean the entire gearbox needs replacing.

Depending on the vehicle, transmission and fault, the problem could involve things such as:

• the mechatronic unit
• clutch operation
• position sensors
• wiring or electrical connections
• hydraulic control
• adaptation or basic settings
• mechanical components within the transmission

This is why an accurate diagnosis can make such a significant difference to the repair.

Replacing an expensive component because it might be responsible for the problem is very different from carrying out testing that demonstrates why that component has failed.

Can you drive with a DSG gearbox fault?

That depends entirely on the nature of the fault.

A transmission that has entered a protective mode, lost gears, is slipping badly or is showing a significant gearbox warning should not simply be ignored.

Continuing to drive a vehicle with a transmission fault can potentially make an existing problem worse, and in some cases the vehicle may not be safe or practical to drive normally.

If your DSG or S tronic transmission has suddenly lost gears, is displaying a gearbox warning or is behaving abnormally, getting the fault diagnosed properly is usually the best place to start.

DSG, S tronic and VAG vehicles

Volkswagen Group uses different names and transmission applications across its brands.

Volkswagen commonly uses the term DSG, while Audi commonly refers to its dual-clutch transmissions as S tronic. Similar transmission technology is also found across Škoda and SEAT models.

The exact gearbox fitted to the vehicle matters, however, which is why a proper diagnosis should be based on the individual vehicle rather than simply assuming that every DSG fault is the same.

The bottom line

If your DSG or S tronic gearbox has suddenly lost a group of gears, is over-revving, refusing to change correctly or showing a transmission warning, don’t automatically assume that you need a complete gearbox.

The symptoms can provide important clues, but the real answer comes from proper diagnosis.

At Boam Automotive, our approach is to investigate the fault, use the available diagnostic information and vehicle data to establish what is actually happening, and then recommend the appropriate repair based on the evidence.

Because when you’re dealing with a complex VAG transmission, guessing gets expensive. Proper diagnosis doesn’t.

Need your DSG or S tronic gearbox diagnosed?

If your Audi, Volkswagen, Škoda or SEAT is experiencing gearbox problems, get in touch with Boam Automotive to discuss the symptoms and arrange a diagnostic assessment.