DSG behavior in Limp Mode (was: perhaps systems should talk to each other)

[cme2c]

My 118TSI DSG was booked in to the dealer for the rattle on startup problem to be fixed. Third trip, but they are keeping it until it's fixed this time. In fairness, the first was the 45000 km service, and the second was for more investigation. Anyway my wife casually mentions the car is down on power and hesitating, and that a light came on that looked like a tap. I suppose the engine check light does look like that, it doesn't look like any engine from this century.

Anyhow VW assist sent the NRMA who cleared the light (code P10A4, which translates to supercharger bypass flap from my extensive googling), and said it was ok to drive BUT the engine still stayed in limp home, which means it won't go over 3200 rpm.

Nobody told the DSG so the car would accelerate, die, change gear, take off again, die etc. Very wearing on the driver.

Now, I reckon I'm smarter than any gear change robot, so I put it into tiptronic. Problem kludged. Until, I'm accelerating on an onramp in third when the robot reckons it's smarter than me, changes down to second, 3600 rpm, no power. The falcon behind nearly hit me (sorry mr falcon driver).

So, VW have very smart programmers. They can make the rear wiper come on when I put the car in reverse, if the front sensor tells the car it's wet. They can stop the engine accelerating if I have my foot on the brake. Why can't they get the ECU to tell the mechatronic unit it's in limp home. huh?

John

PS. I'm not just whinging in VWW, I'm going to email VWA

[Umai Naa!!]

The NRMA shouldn't have cleared the fault code, meaning your dealership now has no evidence to download from the car of when and how the fault occurred and will now have to consume unecessary time to attempt to replicate the fault.

Besides, you drove the car anyway, knowing there was a fault. What did you expect? Yes, both ECUs communicate with eachother, but the Mechatronic ECU still relies on several inputs from the engine ECU to function to a degree.

[AdamD]

I was recently on a drive with a mate in his GTI (to the most recent VW Progression driving course, as it happened), when his car went into limp mode, and we both noticed how badly the DSG deals with the limp mode restrictions. We're both software engineers, and out of curiosity were trying to figure out if the transmission was actually aware of the rpm and power limitations imposed on the motor; as far as we could tell based on observation and plenty of prodding, it wasn't at all.

It's certainly an interesting situation if that is the case. Of course the DSG does continue to operate when the engine's in limp mode, and whilst it doesn't perform ideally, it gets you there.(*)

As an aside, I've renamed this thread so it's easier for people to locate when searching.

(*) Where there should be your dealer.

[cme2c]

The NRMA shouldn't have cleared the fault code, meaning your dealership now has no evidence to download from the car of when and how the fault occurred and will now have to consume unecessary time to attempt to replicate the fault.

Besides, you drove the car anyway, knowing there was a fault. What did you expect? Yes, both ECUs communicate with eachother, but the Mechatronic ECU still relies on several inputs from the engine ECU to function to a degree.

First off, the NRMA was sent by Volkswagen assistance. Secondly, I was driving the car to the dealer when it tried to kill me. Thirdly, the NRMA gave me the fault code before clearing it. I passed the code to the dealer at the time, and the dealer said it was ok to drive, so get off your high horse.

Anyone who has been driving for a long time, and started on cheap cars (because it's all they could afford) learns how to drive around problems. My attempts to do so were thwarted by the software that overrode my selection of 3rd gear.

If the ECU talks to the mechatronic unit, why can't it say "hey, pal, I'm not going over 3000 rpm?" In other words, the limp home mode should be better integrated between the two systems. That's all I'm saying.

John

[cme2c]

Thanks for the retitle , Adam, makes more sense,

John

[grtuned]

First off, the NRMA was sent by Volkswagen assistance. Secondly, I was driving the car to the dealer when it tried to kill me. Thirdly, the NRMA gave me the fault code before clearing it. I passed the code to the dealer at the time, and the dealer said it was ok to drive, so get off your high horse.

Anyone who has been driving for a long time, and started on cheap cars (because it's all they could afford) learns how to drive around problems. My attempts to do so were thwarted by the software that overrode my selection of 3rd gear.

If the ECU talks to the mechatronic unit, why can't it say "hey, pal, I'm not going over 3000 rpm?" In other words, the limp home mode should be better integrated between the two systems. That's all I'm saying.

John

Mate these systems are put in place to provide saftey when a problem occurs so the vehicle can be brought to a dealer or mechanic without leaving the driver stranded!!
You seem to know a little about vehicles so you should be aware of what occurs in limp mode and not try to overide the function by doing this you tried to kill yourself not the car!!!!

[cme2c]

Mate these systems are put in place to provide saftey when a problem occurs so the vehicle can be brought to a dealer or mechanic without leaving the driver stranded!!
You seem to know a little about vehicles so you should be aware of what occurs in limp mode and not try to overide the function by doing this you tried to kill yourself not the car!!!!

1. I was on the way to the dealer when it happened.
2. The dealer had given me the OK to drive, being aware of the particular fault code.
3. I had selected a gear that let the engine work in limp mode.
4. The DSG overrode my selection and took the engine beyond what the ECU considered safe.

It's bad programming.

[cme2c]

Update. VW assist got back to me, agreed it was an unintended outcome in that the DSG should be aware of the reduced rev limit. They undertook to send my concerns back to head office

The car is still at the dealer. They found oil in the inlet, and a cylinder down on compression. They wanted to give it back to me like that, until I asked "is it out of limp mode?" "No, it won't come out of limp mode". It's still there. More in the relevant thread.

Apologies to Umai Naa! and grtuned. Either you are smarter than the dealer or the dealer wanted me to REALLY blow the engine up so they could get a new one.