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VW MKV-A5 Golf/Jettas Discussions area for A5/MkV Jetta/Golf (2005/2006 PD and 2009 CR).

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Old July 9th, 2018, 08:22   #1
shizam
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Default DSG Lag caused by brake switch?

Hey everyone.


I have a still new to me mk5 golf TDI with a DSG transmission. It has a very noticeable lag when you take your foot off the brake and then apply gas. I know this has been discussed to death, but I am trying to see if I can improve it a little.


I have a question for those of you who have a similar car.


I have found that when I have the car running, in Park, when I step on the brake, the little green foot symbol goes out *immediately*. However, when I release the brake pedal quickly, it takes almost a full second for the green foot symbol to turn on. Even though he pedal itself snaps up. I have also checked with VCDS and can hear the transmission selector lock reengaging at the same time the green foot comes on....as it should, just a bit slow.



Given the DSG, and drive by wire throttle, have brake switch sensor inputs and will not accelerate while it thinks the brakes are applied, I think it is possible that lag in the sensing of brake release is making the infamous DSG start from a standstill worse.


Can anyone else check to see if their Mk5 does the same thing when you release the brake pedal quickly?


PS my Golf has no external brake pedal brake switch sensor. The only sensor is the one incorporated into the master cylinder plunger/hall effect sensor on the engine side of the firewall.


Might be clutching at straws......but may be able to improve one of the DSG headaches we all love so much.
Cheers
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Old July 9th, 2018, 11:19   #2
oilhammer
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Why not watch the M-unit's data for the brake pedal switch input and see if it stays ON longer than you think it should.

This is the first I have ever heard anyone complain about this. But your description at least makes sense, and the hydraulic style switch *could* I guess have a wee bit more lag time if it is sticking somehow, whereas the older pedal switch type not so much.
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Old July 9th, 2018, 19:59   #3
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Hey Oil Hammer


I did cycle the pedal with the data showing in VCDS. The VCDS display changes in sync with the "green foot" symbol and the sound of the servo for the transmission selector engaging and disengaging.


I have also cycled the brake while watching the actuator rod for the master cylinder ( under the pedal). The rod *seems* to follow the pedal and not lag it returning to the "pedal up" position.


The fact that the Green Foot light goes out *instantly* when I step on the brake, would seem to indicate it is not a refresh rate delay or bad sensor.
I had hoped the plunger was slow returning as then I would be able to at least have an idea where to start.


As far as I understand it, the hall effect sensor has only 2 modes. Near and far ie pedal pressed or not. There are however 2 different signals processed by the pedal (could be at a software level) 1 for brake light activation and one for transmission/green foot. If you slowly press or release the pedal the two different VCDS 0s change to 1s at a different time in VCDS. I think most likely there is an instantaneous raw signal for the brake lights, but there may be a software imposed delay for the transmission signal ( or it is waiting for something in the DSG to respond) before the Green foot goes out and the trans selector relay releases the shift lever.


I'll have a play with it and report back. I'm hoping to get some feedback from some people so I can see if all the cars do this or if only mine is slow...
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Old July 10th, 2018, 04:52   #4
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Well you are probably the only person in North America with a car exactly like yours.

The only thing we would have to compare to, in regards to the master cylinder mounted brake light switch is the late 2006+ A5 cars, and I am not sure if they all would use the same setup or not. Plus, DSG+ PD TDI would be JUST late 2006 BRM Jettas.
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Old July 10th, 2018, 05:41   #5
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My guess is that the brake prox (Hall Effect) sensor (you stated the brake master cylinder has one) does have at least 3 logic states. On the M/T cars, the clutch prox sensor reacts that way.
  • Near - CC OK to engage
  • Not Near - Disengage CC
  • Far - starter OK to engage
Being the brake has a Prox sensor it probably have those same 3 states and are just used for different purposes on the DSG.

The reason for prox sensors instead of switches is that unless it is damage, a prox sensor will work reliably almost forever because there is nothing in them to wear out such as a plunger or switch contacts.

A software imposed delay would be reasonable because you would want the brakes completely released before the transmission moves the car. The hard part is figuring out if what you are observing actually points to a problem or not.
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Old July 10th, 2018, 10:40   #6
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A little more info on the brake light sensor:
Quote:
Originally Posted by Ol'Rattler View Post
Even though VW calls it a switch, It's actually a proximity sensor much like a crank position sensor and has no moving parts. It is bolted to the outside of the master cylinder.
https://www.idparts.com/brake-light-...lf-p-5045.html
Technicle description:
https://www.ia.omron.com/data_pdf/gu...y_tg_e_6_2.pdf
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VCDS Hacks: DRL Disabled-Seatbelt Chime Disabled-Key fob Power Windows
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Old July 11th, 2018, 20:11   #7
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Thanks guys.


I guess I wont be able to get any feedback on whether this is normal or not.....Since nobody else in the USA will have this type of brake switch setup. I might try this question on a UK forum. The car is an 06 golf tdi with a 16 valve BKD engine. It is RHD and is more Euro than north American.



Most prox sensors I have dealt with are binary. If it is a 3 position sensor, which would make sense given the indications in VCDS, then there could be a tiny lag in the Master Cylinder actuator...just in the last bit of travel. Possibly a clean of the master cyl rod and steel braided brake lines would help return it to the off position quicker, when released.



Maybe I could pull the harness off it and count wires to see how many positions it looks for.


Thanks for the help guys. Looks like it's time to put down the Laptop and get my hands dirty to figure this out.
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Old July 12th, 2018, 07:14   #8
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Quote:
Originally Posted by shizam View Post
Thanks guys.
I guess I wont be able to get any feedback on whether this is normal or not.....Since nobody else in the USA will have this type of brake switch setup. I might try this question on a UK forum. The car is an 06 golf tdi with a 16 valve BKD engine. It is RHD and is more Euro than north American.
Most prox sensors I have dealt with are binary. If it is a 3 position sensor, which would make sense given the indications in VCDS, then there could be a tiny lag in the Master Cylinder actuator...just in the last bit of travel. Possibly a clean of the master cyl rod and steel braided brake lines would help return it to the off position quicker, when released.
Maybe I could pull the harness off it and count wires to see how many positions it looks for.
Thanks for the help guys. Looks like it's time to put down the Laptop and get my hands dirty to figure this out.
No, actually since the A5 on, dubs have been CanBus and LinBus networked and the prox switches on the brake and clutch are a part of the digital technology. It's just that most people don't understand the technology so they pretend it doesn't exist. I thought the statement: "Well you are probably the only person in North America with a car exactly like yours" was pretty hilarious because the technology has been in use since the A5's.

Since you already have the VCDS, find someone with an A5 or newer car with DSG and that would be willing to let you observe the measuring blocks in question. What you might be seeing isn't necessarily the sensor changing state, but the resulting command after a one second or so inhibit.

Also you could "slug" (trick) the sensor with a piece of metal. What you would do is remove the sensor from the master cylinder and gently pass a piece of metal back and forth across the sensing side of the sensor and watch the measuring blocks. On aircraft we could fake the airplane into "air mode" by "slugging" some prox sensors on the landing gear. Our slugs looked a lot like pieces of hacksaw blade.

Are you sure the sensor is reading the push rod? On the clutch, it seemed like the target may have been on the piston inside the clutch master cylinder, but I don't know because I didn't actually take the clutch master cylinder apart.

Please expand about what you know about prox switches. How many wires are used to do the 3 state thing? Is it 2 sensors in one housing or does it do some kind of CAN high/low thing with 2 targets?
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DC stage 1 SMF Clutch
Draw-Tite hitch
Dash Tray
Blue tint aspherical mirrors
Euro Cupholder
Euro Light Switch
2nd grocery hook
VCDS Hacks: DRL Disabled-Seatbelt Chime Disabled-Key fob Power Windows
Adjusted Cam to Crank Timing

Last edited by Ol'Rattler; July 12th, 2018 at 07:29.
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Old July 12th, 2018, 07:43   #9
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Show me someone else in North America with a German-built A5 Golf TDI. (hint, all of our A5 Golfs were called Rabbits, and they all had a 2.5L 5 cyl gasoline engine.... the GTI version had a 2.0L turbo gasoline engine.... the R32 had a 3.2L VR6 gasoline engine).

Also, I never said he was the only one with that particular brake lamp switch. Reread my post please before any more hilarity continues.
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Last edited by oilhammer; July 12th, 2018 at 07:45.
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Old July 12th, 2018, 14:15   #10
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Quote:
Originally Posted by oilhammer View Post
Show me someone else in North America with a German-built A5 Golf TDI. (hint, all of our A5 Golfs were called Rabbits, and they all had a 2.5L 5 cyl gasoline engine.... the GTI version had a 2.0L turbo gasoline engine.... the R32 had a 3.2L VR6 gasoline engine).

Also, I never said he was the only one with that particular brake lamp switch. Reread my post please before any more hilarity continues.
O.K. Apparently his car is a Canadian 2006 A5 TDI with a DSG and has CanBus and LinBus networked components just like our 2006 A5 TDI's have. I read something into your statement that was not what you meant. My bad for that.

My point with all this is that these cars do not have a brake light switch even though VW sometimes calls the brake light sensor a switch. The brake lights are turned on by the lighting controller which receives it's signal from the brake light proximity sensor on the side of the master cylinder which works much like a Hall effects sensor.

Another interesting fact about these Digital cars is that VW got running light brightness and brake light brightness out of a single filiment bulb by using PWM (Pulse Width Modulation) which in it'self is pretty amazing technology for an automobile.
https://en.wikipedia.org/wiki/Pulse-width_modulation

Piece. Keep up the good work which is much appreciated around here.
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2006 Jetta TDI
5 speed, Manufactured 06/06
DC stage 1 SMF Clutch
Draw-Tite hitch
Dash Tray
Blue tint aspherical mirrors
Euro Cupholder
Euro Light Switch
2nd grocery hook
VCDS Hacks: DRL Disabled-Seatbelt Chime Disabled-Key fob Power Windows
Adjusted Cam to Crank Timing
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Old July 30th, 2018, 06:32   #11
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"Please expand about what you know about prox switches. How many wires are used to do the 3 state thing? Is it 2 sensors in one housing or does it do some kind of CAN high/low thing with 2 targets?[/QUOTE]




My prox sensor experience is all aviation related as well. The ones I have seen are just Near Far indication. Like your landing gear example.


From what I have been able to find, in VW literature online, there is a pickup outside the brake master cylinder. Inside the master cylinder either the pushrod for the brake actuator or most likely the master cylinder piston itself has a permanent magnet which is picked up by the external sensor.
The "3 states" comes from monitoring the brake switch raw info in VCDS. If you aren't touching the brake pedal there is one set of 1s and 0s. As you start to depress the pedal slowly, there is another indicated state, then another at a slightly lower pedal position. (0s change to 1s at two different points). If you pause between them, it stays at the lightly depressed state.
It is possible that 1 signal is for brake lights and one for the transmission through Canbus. ie the first change gives brake lights and the second one tells the canbus that the brakes are applied for DSG purposes.



I like the hacksaw bit idea, if I can get it in there to try, as this would help isolate the issue to either mechanical or software. Might be magnet on a stick diagnosis time.


Also I will try to find another similar VW to try.



I'm still out of country so I haven't been able to dig into this any further or count wires. I will post back as I figure out bits. I'll need to find some guinea pig brake pedals to play with in similar cars.


Oh and the car is a German built, New Zealand market machine. The brake sensor looks like this one


https://www.pelicanparts.com/techart...ght_Switch.htm



Thanks
S
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Old July 31st, 2018, 11:48   #12
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Quote:
Originally Posted by shizam View Post
The "3 states" comes from monitoring the brake switch raw info in VCDS. If you aren't touching the brake pedal there is one set of 1s and 0s. As you start to depress the pedal slowly, there is another indicated state, then another at a slightly lower pedal position. (0s change to 1s at two different points). If you pause between them, it stays at the lightly depressed state.

It is possible that 1 signal is for brake lights and one for the transmission through Canbus. ie the first change gives brake lights and the second one tells the canbus that the brakes are applied for DSG purposes.
The "raw data you refer to is called Measuring blocks in VCDS for those that don't know.

Not exactly 2 different signals me thinks. More like 2 different messages on the CanBus network. I'll have to look at the WDM (wiring diagram) to understand that better. Its a shame that in the pic for the prox sensor you can't see how many terminals there are.

In regards to aircraft, the B787 is CanBus and they went bonkers with prox sensors. On the landing gear they were able to throw away a bunch of sequencing valves and make the hydraulic system simpler because of the CanBus and prox sensors. On the brakes, they threw away all of the hydraulics and went with digitally controlled electric brakes.
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DC stage 1 SMF Clutch
Draw-Tite hitch
Dash Tray
Blue tint aspherical mirrors
Euro Cupholder
Euro Light Switch
2nd grocery hook
VCDS Hacks: DRL Disabled-Seatbelt Chime Disabled-Key fob Power Windows
Adjusted Cam to Crank Timing

Last edited by Ol'Rattler; July 31st, 2018 at 11:53.
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Old August 1st, 2018, 20:02   #13
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It is strange that the green brake pedal warning light takes a moment to turn on after releasing the pedal quickly. Possible the switch needs adjustment maybe? Or the pedal itself sticks a little?

I do know that the DSG seems to be more concerned over brake master cylinder pressure rather than the brake switch signal. I've driven a number of them and can get them to preload the clutch before the brake pedal is fully released just by very gradually releasing the pedal, yet the brake lights and signal to ECM that the brake pedal is applied are still on.

I suspect there is a lot of talking between the ABS module and mechatronics unit via CAN Bus, this way the mech unit also knows what incline or decline the car is on and change behavior accordingly. Likewise, since these cars were all equipped with stability control, there is also a pressure sensor (not a switch) in the brake master cylinder. I don't know for sure, but I have my suspicions that the transmission/mechatronics unit are taking into account that reading as well.

Of course most DSGs that I find are extra hesitant are usually ones either low on fluid or at least in need of having the basic settings re-run, possibly both.
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Old September 14th, 2018, 04:58   #14
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Thanks for all the input everyone. I just wanted to close the loop on this thread.
I managed to test out a couple of similar vintage VWs and they all seemed to have similar lag for the "foot light" going off. The actual brake lights are instantaneous. In ETKA, the hall effect sensor on the master cylinder is referred to as "brake light sensor"...for whatever that's worth.



The initial problem, of transmission/clutch engagement lag when taking my foot off the brake and accelerating, is fixed.
I took a long shot and it worked.

I replaced the pendulum (dog bone) mount and both the sub frame bushes. The old one was definitely worn. The problem persisted.....but... After my wife beat on the car for 3 weeks, the problem has cleared. I think the DSG adaptations have compensated for the new engine mount and cleared ( or at least significantly improved) the issue.
I'm not 100% sure that is why it fixed itself, but the problem is definitely gone..... The only change I made was the mount.
Cheers
S
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Old September 19th, 2018, 22:10   #15
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Whoa thatís weird one. I have the ECS inserts for the the dogbone.. definitely improved responsiveness, however DSG lag after coming from a brake hold still persists.




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