Doctor Diesel

DSG Problems

Hello Doctor,


You may remember me from three years ago with the SEAT Altea which kangaroo-ed and stalled. Well, the garage found no fault, even after I paid £200 to have the oil changed, so I traded it in for a pre-registered SEAT Leon Technology 2.0TDI DSG ñ what a mistake! I now have problems with this car. 


It has only done 8,000 miles, and three times on reversing slowly into my garage, it has come out of gear, and then gone back in again. I have it booked into the SEAT dealer in two weeksí time, but am a bit wary that once again they will find no fault and I will once again look like a numpty. I hope to get rid of this car in May next year and get a Toyota Yaris Hybrid, so do I keep the appointment, or soldier on and hope it does not fail completely, which it may not, as it has only happened three times. 


There is also another fault that they canít find ñ the stop-start off button switches off when I have switched it on, and I think it is the switch, but all they do is put it on the diagnostic computer and it says no fault!


I am not happy with this car and miss the Altea, even with all its problems. Can you please help me as to what to do? I am leaning towards cancelling the appointment. Your thoughts please. 


Regards, Robin Chapman


Hello Robin,


Nice to hear from you again, although perhaps not in these circumstances! Yes, I do now remember the Altea, and the associated DSG problem. I think, if I were you, I would try and find the time to repeat the “reverse into garage slowly” manoeuvre in your Leon quite a few times and see with what frequency it actually happens. If you get something better than, say, 1 in 5 when it drops out, then I would take the car in. If these electronic diagnostic systems were all as good as they ought to be, then such incidents would be recorded in the ECU memory, and there would be proof of the incidents, and possibly some form of identification of the cause. This might in fact turn out to be the case, and they may discover a recorded fault code such as “Unexpected/ Implausible Mechanical Gear Disengagement P2711-004î or something similar. 


On reflection, I do think you need to take the car in, if it has not been in previously for this problem. If you were to leave it and do nothing, you might have warranty problems. If you later confessed that you had had the problem a while and done nothing about it, and then it got worse, so you then had to take it in. I know you are possibly not wanting to get deeply into the mechanical/electrical side of things of the DSG, but the information below will put you a bit more in the picture, if you can be patient enough to plough through it!


ìThe Mechatronics, as they call the DSG control components, are all housed in the gearbox, surrounded by DSG oil. They make up the central control unit. All the sensor signals and signals from other control units come together at this point and all actions are initiated and monitored from here. The unit has 12 sensors, by hydraulic means, it controls or regulates eight gear actuators via six pressure modulation valves and five selector valves, and it also controls the pressure and flow of cooling oil from both clutches. The gears are selected via selector forks in the same way as a manual gearbox. Each selector fork selects two gears. The forks are actuated hydraulically on the direct shift gearbox, not selector rods. Many times, the failures begin with temperature sensors failing, either failing outright or falling out of specification. Many sensors have backups, so that if the main sensor fails, a backup sensor will provide the data to the computer. If the data sent is incorrect, the computer will do what it thinks is right based on that incorrect data; hence, failures result. You may only be able to operate in certain gears or none at all. Usually, if a sensor fails, only that section impacted by the sensor is affected. If a sensor fails for second gear, you will not be able to use that gear. Sender G509, a key sensor, can be found in the housing of gearbox input speed sender G182. It measures the temperature of the DSG oil at the outlet of the multi-plate clutches. It operates in a temperature range of ñ55 degrees Celsius to +180 degrees Celsius. If G509 fails, the backup sensors may be able to prevent catastrophic loss. But if they fail, the transmission will go into self-protect mode and you will be stranded. If your transmission suddenly starts to shift into odd gears or the car stops, it could be the N92 solenoid valve inside the mechatronics unit which controls gear activation.î


That’s some fairly detailed advice from a transmission expert, and some or maybe none of it is relevant, but it may help you understand some of the operations. 


The stop/start disengage buttons fitted to cars are sometimes rather confusing. You have to press the button and make the light come on to disable the stop/start function, and the engine has to be going for this to take effect. If you are having problems with the stop/start not working at times, that’s a whole different story related to state of battery charge and so on. 


Hope the reply is helpful, and please keep me updated. I would very much like to know the outcome.


Best regards, 

Doc Diesel


To which Robin later replied:


Hi Doc,


Well it was much as expected, and no fault was found. The head of service reception agreed that it was best to keep the appointment, as it is now logged, and if a problem occurs, I did let them know that there could be a fault. The stop/start button has been behaving itself lately! Thanks for your DSG information, I did read all of it! 


Regards, Robin


No surprise really, but I’ll keep readers updated. As I wrote to Robin, the 6-speed DSG that comes with the 2.0-litre TDI in your Leon is the more robust one, with the clutches running in oil, and this unit is generally pretty trouble-free. Don’t hesitate to demand action under warranty if the problems keep surfacing. If such should unfortunately happen, it might support your case if you kept a record of the mileage and date on each occasion happens. To me, it would seem to be either a problem with the electronics (when you might expect a fault to be recorded), or one with the selector unit, or its associated wiring, when a fault code might be less likely. 


Do please keep me posted. Hope the Leon is pleasing you otherwise though. It’s normally a really nice car. 


Best regards Doc

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