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A further look at the DSG

After completing a basic diagnostic routine, here are the places to look for potential problems
Wednesday, July 30, 2014 - 07:00
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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.

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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.

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