A further look at the DSG

July 30, 2014
In this article, attention is given to the DQ250 commonly known here in United States as the DSG 02E gear box.

In the July issue of Motor Age, we took sometime to discuss the DSG, specifically the DQ200 dual dry clutch unit covering typical failures encountered with this transmission. Reprogramming the Mechatronic unit with modified software from TVS resolved many of these failures. Much of this information was dedicated to the online, international POWERTRAIN PRO readers.

In this article, attention is given to the DQ250 commonly known here in United States as the DSG 02E gear box (Figure 1). TVS comments that of all the varieties of Volkswagen’s DSG gear boxes, this is the best one. That doesn’t mean its problem-free either. This too has programming in need of modifications, which will in part be covered in this article.

Before we do, aside from pulling codes and making fluid level and condition checks, it always is good to perform the following checks and procedures as a preliminary diagnostic routine.

FIGURES 1-4

  1. Check wheel speed signals as the ABS interacts with the Mechatronic unit and can contribute to a malfunction (The Mechatronic unit is the computer and valve body combined as seen in Figure 2).
  2. Check engine load sensors and related filters (fuel, air, etc.). Skewed sensor information will affect the engine computer’s ability tocalculate engine torque. This information then is delivered to the Mechatronic unit to control clutch apply pressure. The Mechatronic unit also measures engine torque by how much pressure is required to maintain a 1 percent slip on the fully applied clutch. Wrong data can affect this operation.
  3. The dual mass flywheel can cause noise and clunk complaints (Figure 3). Listen for noise coming from between the engine and transmission. The clutch drum assembly can also cause clunk shifts. The clutch drum drive cover snap ring is known to pop out of its groove (Figure 4). This is not to be confused with the sealing cover (Figure 5). The drive cover is located behind the sealed cover. The actual double clutch drum is held in position by a small heavy snap ring. The drive cover indexes to the double clutch drum (Figures 6 and 7). When the drive cover snap ring pops out, this cover does not have too much room to travel, so it bounces between the sealed cover and the double clutch drum assembly causing the clunking sound on the shifts. 
  4. Perform Basic Settings with a capable scan tool or lap top based program.

Software updates, basic settings and oil changes are useless in 96 percent of the cases when a gearbox has a real problem, unless the gearbox has had no new oil in about 124,000 miles.

FIGURES 5-7

With these preliminary diagnostic routines now discussed, the problems encountered with this box are the Mechatronic unit, a failed clutch assembly and bearing failure, though this is very rare. Although TVS hears from others that they see bearing problems, they themselves see only a few a year.

When these DSG units begin to fail, the shifts become very clunky. It can be due to programming issues, clutch drum problems or that something is wrong inside the transmission. TVS engineering feels it is better to replace what is needed rather than rebuilding it. From their experience, it is better to just change the Mechatronic assembly, the clutch drum assembly or the main gear box with a new one. It seems that once you disassemble these transmissions, after repairs and installation, the transmission never seems to shift right. In fact, they partially disassembled a new transmission, reassembled it and installed it into a vehicle. The result was a noisy gearbox. After driving it approximately 620 miles, the noise did quiet down some but still remained very noticeable. For this reason, TVS has concluded that opening a DQ250 is not a very good idea, particularly so if you have a customer that complains about everything. There will be noise and it will not shift as smooth as it once did.

This is especially true with the 4-wheel drive version, as it already is inherently noisy and clunky, and unexplainably so. You can use all new parts, torque everything perfectly with all proper clearances and you will still have noise and clunk issues in many cases. They had a brand new 2-wheel drive transmission that was shifting smoothly and had no noise. They converted it to a 4-wheel drive setup with minimum necessary parts and it had noise. It also resulted in a very harsh engagement into Drive or Reverse.

Another problem that can be experienced occurs in vehicles using 2.0L TDI engines. The driver accelerates up to 4th gear at 2,000 rpm when the turbo kicks in hard and you feel a heavy vibration in the car. It feels like a bad fuel injector. Replacing the clutch assembly helps about 35 percent of the time. Besides clutch issues being the cause in some cases, these assemblies might have torsion spring problems as well. Other times there migh be fluid to friction issues, which by changing the fluid might help. It does not completely eliminate the problem, but it does help. If changing the clutch assembly eliminates the problem, it might come back again approximately 6,200 miles later with the same complaint. The shudder complaint usually occurs after a highway run and the transmission is hot. Once you are back into city driving the shudder comes back again.

Sometimes changing the Mechatronic assembly also can help, but the real problem has to do with programming. When fully applied the clutch is programmed to have a 1 percent slip.  If it doesn’t see that slip, it will lessen the apply pressure. Then when it slips too much, it increases pressure. The cycling of the clutch in an attempt to maintain a 1 percent slip causes the heavy vibration throughout the vehicle. In time it causes damage to the friction plates and properties in the fluid break down as well. TVS reprograms the Mechatronic unit with a modified slip ratio to resolves this problem.

Just a bit more on this closed loop system, using engine management software as an example; it has a fuel map targeted to obtain a 14.7 to 1 air fuel ratio. Through oxygen sensor input, the system constantly adjusts fuel delivery to maintain the ideal 14.7 air fuel ratio.

Similarly, the Mechatronic unit receives input that the engine controller is calling for 300Nm of torque. The Mechatronic unit calculates that 116 psi (8 bars) of pressure will be needed to maintain a 1 percent slip, i.e., when engine rpm is 2,500, input shaft 1 or 2 rpm will be 2,475. By preset values such as this, the Mechatronic unit quickly can adjust clutch pressure to meet engine torque while constantly maintaining a 1 percent slip. If it notices a zero percent slip with 116 psi, it begins to drop pressure and sees that at 109 psi (7.5 bars) it sees the 1 percent slip. The Mechatronic is learning and then adapts to a new preset value of - 7 psi (-0.5 bars) for the next time 300Nm of torque is required.

This adaptation value, however, is not presented in psi or bars; it is presented in amperage and frequency percent of the clutch solenoid. The computer will decrease or increase amperage via frequency to raise or lower clutch pressures so one might see a -0.15 amps as an adaptation value. Again, within the program there are tables that cross reference data of preset values to quickly respond to real time driving. This is done for acceleration, deceleration, high, medium and low loads as well as creep modes (when you are driving just a few miles per hour). 

One complaint often times voiced by the driver is that acceleration from a stop seems slow. You can burry the pedal yet the vehicle will accelerate slower than expected. The reason for this is to keep torque increase relative to clutch pressure. They both build up slowly so everything goes smoothly. This is considered normal.

There is an option called a launch control for those who want a faster acceleration for racing. This is not a standard option in every vehicle here in the U.S. Launch control is when you select sport mode and deactivate stability control, then stand on both the break and the throttle simultaneously; the engine will ramp up to about 3,000 rpm. As soon as you release the brake pedal, the computer will manage the torque and close clutch to provide a maximum zero to 60 performance.  

But even this is slower than what is desired, and TVS developed a program to shorten the lag time without compromising the clutch. Their launch control operates from the manual shift mode. They removed the annoying half-second delay time normally observed on launch, pumping 174 psi (12 bars) into the clutch. It becomes so strong that it wants to push the vehicle through the brakes.

Another software issue that occurs is during deceleration. Some newer software with added features affects the way it assists breaking the vehicle through “engine braking.” Some earlier versions lacking these added features allowed for smoother deceleration. When a new Mechatronic unit is installed, they now have a more pronounced engine braking occurring during deceleration, which they have not had before. Additionally, you can have two vehicles the same year, make and engine size yet this feature will act completely different between the two vehicles. The Mechatronic unit interacts with the engine’s software of which there can be differences, thus causing a problem in one of the vehicles and not the other. Once again, reprogramming the Mechatronic unit will be required to eliminate the rough downshift feel the driver will complain about.

There are several other shifting complaints that are considered normal for this double clutch transmission. One of which is shifting from 5th to 6th and back to 5th. Under certain driving conditions, it is difficult for the transmission to make this transition smoothly. The action it takes to make the shift is perceived as a slip.

Delayed Tiptronic down shift control is another. This too is considered normal operation, as this requires multiple declutching. Certain synchronization speeds must be reached for declutching to take place, which can be as long as one second.

One other point to make relates to parking the vehicle. A contributing factor in causing premature failure of the transmission is to place the vehicle into Park before applying the power brake. We have seen parking pawls snap as a result of this incorrect procedure. The proper procedure is to apply the power brake first then place the selector lever into Park.

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