DSG DQ381 and DQ500 – P1735, P1736 Faults, Loss of Gears and Mechatronic Repair

Has the DSG transmission suddenly lost even or odd gears, entered emergency mode or displayed a transmission malfunction warning? In vehicles equipped with DQ381 and DQ500 gearboxes, one possible cause is a fault in the mechatronic unit or an incorrect position signal from the components responsible for selecting gears.

Fault codes including P1735 or P1736 may be stored in the transmission control unit. This does not mean that a sensor, complete mechatronic unit or entire gearbox should be ordered based on the fault code alone.

The exact fault description, status, freeze-frame data, controller version and actual gearbox behaviour must first be established. Similar symptoms may result from a sensor fault, TCU electronics, electrical wiring, the hydraulic section of the mechatronic unit or a mechanical problem inside the transmission.

Symptoms of DQ381 and DQ500 DSG Failure

The symptoms depend on the type of failure and on which section of the gearbox has been disabled by the controller.

The most common symptoms include:

• loss of some even or odd gears,
• the DSG entering emergency mode,
• inability to engage a selected gear,
• the gearbox remaining in one gear,
• the vehicle being unable to move,
• a sudden jerk immediately before the fault appears,
• a flashing transmission-position indicator,
• a “gearbox malfunction” warning or similar message on the instrument cluster,
• faults returning after they have previously been cleared.

The loss of one group of gears is related to the design of a dual-clutch transmission. The gearbox has two power paths and two clutches. If the controller cannot reliably determine the position of one section or operate it safely, it may disable the relevant part of the transmission.

P1735 and P1736 – What Can These Faults Mean?

In DQ381 and DQ500 gearboxes, P1735 and P1736 are often associated with problems involving the position control of one of the two transmission sections. The exact description and fault-code extension may vary depending on the controller and software version.

For this reason, we do not analyse only the basic DTC number. We also check:

• the complete fault description and extension,
• whether the fault is intermittent, static or currently active,
• the number of recorded occurrences,
• the conditions under which the fault was stored,
• transmission temperature at the time of failure,
• vehicle-system voltage,
• specified and actual positions of the gear-selection components,
• gearbox behaviour during an attempt to perform basic settings.

The same fault code may lead to different conclusions depending on the transmission version, software and measurement results.

Does P1735 or P1736 Always Mean a Failed Sensor?

No. A position-sensor fault is one possible cause, but it is not the only one.

Other possible causes include:

• damage to the mechatronic control electronics,
• an open circuit or short circuit in the signal wiring,
• a power-supply or ground problem,
• damage to an internal electrical connection,
• contamination or damage in the hydraulic section,
• incorrect mechatronic hydraulic pressure,
• binding or excessive resistance in the gear-selection mechanism,
• damage to selector forks, synchronisers or other mechanical components,
• the result of an incorrectly performed previous repair,
• incorrect software or an incomplete programming procedure.

If a mechanical component cannot reach the required position, the controller may store a fault related to its position signal even when the sensor itself is still operating correctly. Replacing the sensor without checking the mechanical system will not solve the problem in such a case.

P1735 and P1736 Do Not Automatically Mean the Entire Gearbox Must Be Replaced

After an initial diagnosis, vehicle owners are often told that the complete mechatronic unit or the entire transmission must be replaced. Such a repair may sometimes be justified, but the decision should be based on measurements and inspection rather than on the fault code alone.

Depending on the type of damage, possible solutions may include:

• repairing the original mechatronic unit,
• repairing or replacing the failed measuring component,
• repairing the electrical circuit,
• repairing the hydraulic section,
• repairing the mechanical part of the gearbox,
• replacing the mechatronic unit where repair is not technically justified,
• programming and matching another controller where required.

Not every mechatronic unit can be repaired safely. The decision depends on the extent of the damage, the condition of the controller, previous work and the availability of suitable components.

How Do We Diagnose DQ381 and DQ500 Gearboxes?

The diagnostic procedure is selected according to the symptoms and vehicle condition. We proceed differently when the fault is continuously active than when it occurs only occasionally after the gearbox has warmed up or under higher load.

Depending on the case, the procedure may include:

• a complete scan of all vehicle control units,
• identification of the gearbox, mechatronic unit and software version,
• analysis of freeze-frame data and fault-recording conditions,
• checking supply voltage and electrical connections,
• analysis of the actual positions of gear-selection components,
• checking clutch adaptation values,
• assessment of temperature and hydraulic parameters,
• checking transmission-fluid level and condition,
• attempting basic settings where the gearbox condition allows it,
• a road test with live-data recording,
• removal of the mechatronic unit and further bench inspection.

Not every listed step is required in every case. If the vehicle cannot move or the fault is permanently active, the sequence of work will differ from a fault that occurs once every few weeks.

DQ381 and DQ500 Mechatronic Repair

Once the fault has been confirmed, we remove the mechatronic unit and assess its actual condition. We do not assume in advance that replacing one sensor will be sufficient.

The scope of repair may include:

• removing the mechatronic unit according to the procedure for the specific gearbox,
• inspection of the electronic controller,
• checking sensors and measuring circuits,
• inspection of the circuit board and internal electrical connections,
• verification of the hydraulic section,
• assessment of solenoid valves and oil passages,
• repair using suitable-quality components,
• replacement of required seals and single-use parts,
• restoring or transferring controller data where required,
• installing the mechatronic unit and filling the gearbox with the correct fluid,
• performing basic settings and adaptations,
• checking operating data and carrying out a verification road test.

Controller cloning is not a mandatory part of every repair. It is used only where required by the type of damage, controller design and selected repair method.

Transmission Fluid and Filters After Mechatronic Repair

The required fluid service depends on the transmission version, scope of work and condition of the fluid. We do not simply top up the gearbox with an unspecified fluid after installation.

We check, among other things:

• whether the fluid meets the requirements of the specific transmission,
• whether the fluid contains metallic particles or signs of overheating,
• whether the system was contaminated during a previous repair,
• which filters and seals require replacement,
• which fluid-level procedure applies to the specific gearbox version.

An incorrect fluid level, unsuitable oil or contamination can interfere with mechatronic operation and affect the result of the adaptation procedure.

Basic Settings and Road Testing After Repair

Repairing or installing the mechatronic unit does not complete the job. The controller must correctly recognise the positions of the actuators and the operating characteristics of the clutches.

Depending on the transmission version and scope of repair, we may perform:

• the required guided diagnostic functions,
• gearbox basic settings,
• adaptation of clutches and gear-selection actuators,
• monitoring fluid temperature during the procedure,
• verification of values after the adaptation is completed,
• a road test under different load conditions,
• a further fault-code and live-data check after the test drive.

If the basic settings cannot be completed successfully, they should not be repeated indefinitely. The reason the controller cannot achieve the required positions or values must be identified.

DSG Repair and Shift Points Modification Are Two Different Services

Mechatronic repair must not be combined with shift-point modification as a way of removing a fault.

Software cannot repair a failed sensor, controller, valve, clutch or mechanical transmission component.

Shift Points modification can only be considered after the gearbox has been confirmed as mechanically and electronically sound, no faults are stored and it passes the required basic settings and road test.

In a correctly operating transmission, an individual strategy modification may include:

• adjusting shift points in Drive mode,
• earlier downshifts as load increases,
• reducing operation at excessively low engine speed,
• improving response to accelerator input,
• making an excessively aggressive Sport mode more usable,
• matching transmission control to a modified engine.

The purpose is not to raise engine speed unnecessarily or hide mechanical wear. The modification should improve cooperation between a healthy engine and a healthy transmission under real driving conditions.

Which Vehicles Use DQ381 and DQ500 Gearboxes?

DQ381 and DQ500 transmissions are used in many Volkswagen Group vehicles with a transverse powertrain layout. The exact gearbox type should always be confirmed using the VIN, transmission code or controller identification.

They can be found in selected versions of models including:

• Audi: A3, S3, RS3, Q2, Q3, RS Q3, TT, TTS and TT RS,
• Volkswagen: Golf, Passat, Arteon, Tiguan, T-Roc and selected Transporter versions,
• Škoda: Octavia, Superb and Kodiaq,
• SEAT and Cupra: Leon, Ateca, Tarraco and Formentor.

The model name alone is not sufficient to identify the transmission. The same model may use different gearboxes depending on the engine, model year, drivetrain and market.

Can the Vehicle Still Be Driven With a DSG Fault?

If the gearbox has lost some gears, entered emergency mode or displayed a serious transmission fault warning, continued driving may worsen the damage.

Driving should not be continued if:

• the gearbox jerks violently,
• the vehicle cannot move off correctly,
• the transmission shifts into Neutral by itself,
• unusual metallic noises are present,
• there is a transmission-fluid leak under the vehicle,
• the fault returns immediately after starting,
• the gearbox operates using only one group of gears.

In this situation, transporting the vehicle to a workshop is safer than attempting to continue driving.

Why Should the Fault Not Be Cleared Before Diagnosis?

Clearing the fault may temporarily restore transmission operation, but it can also remove some of the information needed to identify the cause.

Important diagnostic information includes:

• a complete record of all faults stored in the vehicle,
• fault status and number of occurrences,
• freeze-frame data,
• temperature and voltage at the time of the fault,
• related engine, ABS, power-supply or CAN communication faults.

If a failure has occurred, it is best not to clear faults or perform random adaptations before the vehicle arrives at the workshop.

DQ381 and DQ500 DSG Diagnostics and Repair – Szulc Motorsport

We do not replace parts based on one fault code. We first establish whether the problem involves a position signal, controller electronics, hydraulics or the mechanical section of the transmission.

Only after diagnosis do we determine whether the vehicle requires:

• mechatronic repair,
• mechanical gearbox repair,
• replacement of the controller or complete mechatronic unit,
• transmission-fluid service,
• programming and basic settings,
• further diagnosis of other vehicle systems.

Frequently Asked Questions

Does P1735 or P1736 mean the mechatronic unit is damaged?

The fault may indicate a problem related to the mechatronic unit or the position control of gear-selection components, but the code alone is not sufficient for a complete diagnosis. The full code extension, operating data and mechanical condition of the gearbox must also be checked.

Does the entire gearbox need to be replaced?

Not always. In many cases, the mechatronic unit or the failed component can be repaired. Complete gearbox replacement is justified only where the extent of mechanical damage or the economics of repair support that decision.

Is replacing the sensor enough?

Only if diagnostics confirm that the sensor or its circuit is the actual cause. A similar fault may also occur due to a mechanical or hydraulic problem.

Is adaptation required after repair?

Depending on the scope of repair, basic settings, adaptation of the clutches and actuators and a verification road test may be required.

Can a used mechatronic unit be installed?

In selected cases it may be possible, but hardware and software compatibility must be confirmed and the required data must be transferred or matched correctly. A random controller from a similar gearbox may not operate correctly.

Will Shift Points modification repair emergency mode?

No. Shift Points modification is intended only for a correctly operating transmission. It does not repair P1735, P1736 or mechatronic faults.

Author: Grzegorz Szulc – Szulc Motorsport

Specialisation: ODIS diagnostics, DSG and S-Tronic gearbox repair, mechatronics, controller programming, Shift Points modifications and Volkswagen Group vehicle electronics.