brake issue
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brake issue
hello again guys so my 2007 q7 3.0tdi has developed a issue where the front right hand brake will just apply itself at motorway speeds of 60-80 mph after 10 mins of motorway driving. iv scanned for codes nothing at all just put new disks and pads both brembo, also had not much issue lushing calliper pistons back on that side. its completely fine around town can drive all day with no issues just once in a blue moon when braking hard my pedal will sink to the floor and give my foot some jank feedback its kinda scary.. your help would be appreciated
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hello again guys so my 2007 q7 3.0tdi has developed a issue where the front right hand brake will just apply itself at motorway speeds of 60-80 mph after 10 mins of motorway driving. iv scanned for codes nothing at all just put new disks and pads both brembo, also had not much issue lushing calliper pistons back on that side. its completely fine around town can drive all day with no issues just once in a blue moon when braking hard my pedal will sink to the floor and give my foot some jank feedback its kinda scary.. your help would be appreciated
The following are somewhat commonly encountered issues on the 4L Q7 platform:
ABS sensors most often fail individually, and usually those will throw off fault codes. Loose/worn suspension components and crusty/sticky height sensors can also cause the traction control/ABS system to 'trigger/malfunction' temporarily when car encounters breaks and sudden changes in road surface on the pavement, so if you seeing any temp flashing of the ABS/ESC lamp in dash when the issues occur, then take note. Height sensors on the Q7 do need to be inspected and maintained and can be removed, cleaned & lubricated, as necessary. I just sprayed the movement points for the height sensors while still connected on my Q7 TDI to keep them functional.
Just bear in mind that the symptoms you have are simply manifestations of 'upstream issues', so you have to narrow down the possible root cause issues. Definitely you want/need to use new brake hardware/pad return springs when changing rotors/pads out, and apply brake lubricant to the friction points/brake pad slides, so the system is working as designed after you DIY the brake service. When I do a full brake job, then I also go ahead and replace the brake fluid/fully bleed the system following the TSB protocols.
The vacuum line connect to the engine vacuum line is right at the firewall on passenger side, and the female side of that connection splits/cracks open like a flower over time/heat cycles, etc., thus creating a vacuum leak, which starts very small and progressively gets worse over time. Super easy to check for that problem as those two sides of the connection are designed to fit tightly together. So, if you can simply reach down and pull the engine vac side out of the bottom connector with no real effort involved, then it's leaking vacuum. This will manifest as a soft brake pedal and intermittent loss of brake pedal resistance (goes to the floor), because the brake booster works off of engine vacuum, etc. There is also a simple test for the brake booster itself to ensure it's still fully functional; just another box to check off the elimination list, etc. If you've actually been having the spongy pedal/intermittent pedal goes way down, then that's likely this particular age/heat-cycling of the thermoplastic used for these vacuum line fittings.
Resolution options are you buy the overpriced new vacuum line that leads to brake booster/connects to brake booster, or you directly repair the vacuum lines connection by DIYing the fix via splicing in a new section of hose & connector, or you can use some JB Weld pipe repair 'tape', or similar product to carefully go round and reinforce that connection and eliminate the air leak if the female connector side is still all there.
Saved the worst for last:
ABS pump can have a seal failure allowing air to enter the system; normally related to spongy brake pedal and loss of brake pedal response, etc. This is by no means affecting all Q7s, but does happen on the older /high mileage cars, etc. This is often times misdiagnosed and the ABS pump is replaced, which doesn't fix the symptoms that were actually the result of improper brake bleeding procedure, and/or the vacuum leak noted above.
Warning: Don't replace the ABS pump/expensive bits unless you've verified everything else is 100% good in the braking system (scan car reason), and related ABS/ESC systems. A TSB exists on how to correctly bleed the Q7s brake system, and if you aren't following that TSB procedure exactly, then you aren't doing it correctly, which allows air to remain in the system. Brake fluid change interval is every 2 years on the Q7, and you want to stick very close to that interval, since flushing/bleeding brakes is much less costly than replacing calipers, master cylinder, ABS pump, etc.
Thread Starter
AudiWorld Junior Member
Joined: May 2025
Posts: 34
Likes: 8
Symptoms you described could be related more than one issue, IMO.
The following are somewhat commonly encountered issues on the 4L Q7 platform:
ABS sensors most often fail individually, and usually those will throw off fault codes. Loose/worn suspension components and crusty/sticky height sensors can also cause the traction control/ABS system to 'trigger/malfunction' temporarily when car encounters breaks and sudden changes in road surface on the pavement, so if you seeing any temp flashing of the ABS/ESC lamp in dash when the issues occur, then take note. Height sensors on the Q7 do need to be inspected and maintained and can be removed, cleaned & lubricated, as necessary. I just sprayed the movement points for the height sensors while still connected on my Q7 TDI to keep them functional.
Just bear in mind that the symptoms you have are simply manifestations of 'upstream issues', so you have to narrow down the possible root cause issues. Definitely you want/need to use new brake hardware/pad return springs when changing rotors/pads out, and apply brake lubricant to the friction points/brake pad slides, so the system is working as designed after you DIY the brake service. When I do a full brake job, then I also go ahead and replace the brake fluid/fully bleed the system following the TSB protocols.
The vacuum line connect to the engine vacuum line is right at the firewall on passenger side, and the female side of that connection splits/cracks open like a flower over time/heat cycles, etc., thus creating a vacuum leak, which starts very small and progressively gets worse over time. Super easy to check for that problem as those two sides of the connection are designed to fit tightly together. So, if you can simply reach down and pull the engine vac side out of the bottom connector with no real effort involved, then it's leaking vacuum. This will manifest as a soft brake pedal and intermittent loss of brake pedal resistance (goes to the floor), because the brake booster works off of engine vacuum, etc. There is also a simple test for the brake booster itself to ensure it's still fully functional; just another box to check off the elimination list, etc. If you've actually been having the spongy pedal/intermittent pedal goes way down, then that's likely this particular age/heat-cycling of the thermoplastic used for these vacuum line fittings.
Resolution options are you buy the overpriced new vacuum line that leads to brake booster/connects to brake booster, or you directly repair the vacuum lines connection by DIYing the fix via splicing in a new section of hose & connector, or you can use some JB Weld pipe repair 'tape', or similar product to carefully go round and reinforce that connection and eliminate the air leak if the female connector side is still all there.
Saved the worst for last:
ABS pump can have a seal failure allowing air to enter the system; normally related to spongy brake pedal and loss of brake pedal response, etc. This is by no means affecting all Q7s, but does happen on the older /high mileage cars, etc. This is often times misdiagnosed and the ABS pump is replaced, which doesn't fix the symptoms that were actually the result of improper brake bleeding procedure, and/or the vacuum leak noted above.
Warning: Don't replace the ABS pump/expensive bits unless you've verified everything else is 100% good in the braking system (scan car reason), and related ABS/ESC systems. A TSB exists on how to correctly bleed the Q7s brake system, and if you aren't following that TSB procedure exactly, then you aren't doing it correctly, which allows air to remain in the system. Brake fluid change interval is every 2 years on the Q7, and you want to stick very close to that interval, since flushing/bleeding brakes is much less costly than replacing calipers, master cylinder, ABS pump, etc.
The following are somewhat commonly encountered issues on the 4L Q7 platform:
ABS sensors most often fail individually, and usually those will throw off fault codes. Loose/worn suspension components and crusty/sticky height sensors can also cause the traction control/ABS system to 'trigger/malfunction' temporarily when car encounters breaks and sudden changes in road surface on the pavement, so if you seeing any temp flashing of the ABS/ESC lamp in dash when the issues occur, then take note. Height sensors on the Q7 do need to be inspected and maintained and can be removed, cleaned & lubricated, as necessary. I just sprayed the movement points for the height sensors while still connected on my Q7 TDI to keep them functional.
Just bear in mind that the symptoms you have are simply manifestations of 'upstream issues', so you have to narrow down the possible root cause issues. Definitely you want/need to use new brake hardware/pad return springs when changing rotors/pads out, and apply brake lubricant to the friction points/brake pad slides, so the system is working as designed after you DIY the brake service. When I do a full brake job, then I also go ahead and replace the brake fluid/fully bleed the system following the TSB protocols.
The vacuum line connect to the engine vacuum line is right at the firewall on passenger side, and the female side of that connection splits/cracks open like a flower over time/heat cycles, etc., thus creating a vacuum leak, which starts very small and progressively gets worse over time. Super easy to check for that problem as those two sides of the connection are designed to fit tightly together. So, if you can simply reach down and pull the engine vac side out of the bottom connector with no real effort involved, then it's leaking vacuum. This will manifest as a soft brake pedal and intermittent loss of brake pedal resistance (goes to the floor), because the brake booster works off of engine vacuum, etc. There is also a simple test for the brake booster itself to ensure it's still fully functional; just another box to check off the elimination list, etc. If you've actually been having the spongy pedal/intermittent pedal goes way down, then that's likely this particular age/heat-cycling of the thermoplastic used for these vacuum line fittings.
Resolution options are you buy the overpriced new vacuum line that leads to brake booster/connects to brake booster, or you directly repair the vacuum lines connection by DIYing the fix via splicing in a new section of hose & connector, or you can use some JB Weld pipe repair 'tape', or similar product to carefully go round and reinforce that connection and eliminate the air leak if the female connector side is still all there.
Saved the worst for last:
ABS pump can have a seal failure allowing air to enter the system; normally related to spongy brake pedal and loss of brake pedal response, etc. This is by no means affecting all Q7s, but does happen on the older /high mileage cars, etc. This is often times misdiagnosed and the ABS pump is replaced, which doesn't fix the symptoms that were actually the result of improper brake bleeding procedure, and/or the vacuum leak noted above.
Warning: Don't replace the ABS pump/expensive bits unless you've verified everything else is 100% good in the braking system (scan car reason), and related ABS/ESC systems. A TSB exists on how to correctly bleed the Q7s brake system, and if you aren't following that TSB procedure exactly, then you aren't doing it correctly, which allows air to remain in the system. Brake fluid change interval is every 2 years on the Q7, and you want to stick very close to that interval, since flushing/bleeding brakes is much less costly than replacing calipers, master cylinder, ABS pump, etc.
all the brake caliper components have been replaced I.e brake pads disks and the related wear sensors and retaining spring clip , have no codes at all at any time I sometimes get a traction light when going over some pot holes and could you send over the brake bleed process please I’m leaning towards a bad abs pump I’m fully prepared to fire the parts cannon checked live data all abs sensors appear to work as the should with non dropping out ever that I can see
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If you have Ross-Tech VCDS scan tool, it actually does the bleed process for you.
Open VCDS, go to modules, select ABS module, then under Basic Settings it'll have brakes bleeding. Other scan tools may also support this ABS pump centered, brake bleeding sequence as well, but the VCDS definitely supports it and guides you through the entire procedure step-by-step. Using a pressure bleeder in conjunction is ideal to prevent air from reentering the system via the reservoir/master cylinder, etc., but it can be done via refill the reservoir after each bleed step, etc.
I'll see if I have that VW/Audi TSB bookmarked. The whole point is to focus the actual bleeding process on the ABS pump and leverage it to force out air bubbles trapped inside the ABS pump, as well as the entire system.
You most definitely want to verify that vacuum hose connection (brake booster to engine vacuum line at firewall) is NOT involved, and on an early model car I'd definitely place a bet it is involved. I've had that one happen on my '10 already, temp fixed via duct tape, and when that began to relapse again, I redid it with JB Weld pipe repair tape to both seal it up tight and reinforce that connection point. If mine ever fails in future, then I'll cut out the bad section and insert some new fittings/hose, if the old booster vac hose is still good otherwise, which doesn't seem to be the issue; it's just the heat in engine bay that fatigues the thin plastic on the female connection side.
Open VCDS, go to modules, select ABS module, then under Basic Settings it'll have brakes bleeding. Other scan tools may also support this ABS pump centered, brake bleeding sequence as well, but the VCDS definitely supports it and guides you through the entire procedure step-by-step. Using a pressure bleeder in conjunction is ideal to prevent air from reentering the system via the reservoir/master cylinder, etc., but it can be done via refill the reservoir after each bleed step, etc.
I'll see if I have that VW/Audi TSB bookmarked. The whole point is to focus the actual bleeding process on the ABS pump and leverage it to force out air bubbles trapped inside the ABS pump, as well as the entire system.
You most definitely want to verify that vacuum hose connection (brake booster to engine vacuum line at firewall) is NOT involved, and on an early model car I'd definitely place a bet it is involved. I've had that one happen on my '10 already, temp fixed via duct tape, and when that began to relapse again, I redid it with JB Weld pipe repair tape to both seal it up tight and reinforce that connection point. If mine ever fails in future, then I'll cut out the bad section and insert some new fittings/hose, if the old booster vac hose is still good otherwise, which doesn't seem to be the issue; it's just the heat in engine bay that fatigues the thin plastic on the female connection side.
Thread Starter
AudiWorld Junior Member
Joined: May 2025
Posts: 34
Likes: 8
If you have Ross-Tech VCDS scan tool, it actually does the bleed process for you.
Open VCDS, go to modules, select ABS module, then under Basic Settings it'll have brakes bleeding. Other scan tools may also support this ABS pump centered, brake bleeding sequence as well, but the VCDS definitely supports it and guides you through the entire procedure step-by-step. Using a pressure bleeder in conjunction is ideal to prevent air from reentering the system via the reservoir/master cylinder, etc., but it can be done via refill the reservoir after each bleed step, etc.
I'll see if I have that VW/Audi TSB bookmarked. The whole point is to focus the actual bleeding process on the ABS pump and leverage it to force out air bubbles trapped inside the ABS pump, as well as the entire system.
You most definitely want to verify that vacuum hose connection (brake booster to engine vacuum line at firewall) is NOT involved, and on an early model car I'd definitely place a bet it is involved. I've had that one happen on my '10 already, temp fixed via duct tape, and when that began to relapse again, I redid it with JB Weld pipe repair tape to both seal it up tight and reinforce that connection point. If mine ever fails in future, then I'll cut out the bad section and insert some new fittings/hose, if the old booster vac hose is still good otherwise, which doesn't seem to be the issue; it's just the heat in engine bay that fatigues the thin plastic on the female connection side.
Open VCDS, go to modules, select ABS module, then under Basic Settings it'll have brakes bleeding. Other scan tools may also support this ABS pump centered, brake bleeding sequence as well, but the VCDS definitely supports it and guides you through the entire procedure step-by-step. Using a pressure bleeder in conjunction is ideal to prevent air from reentering the system via the reservoir/master cylinder, etc., but it can be done via refill the reservoir after each bleed step, etc.
I'll see if I have that VW/Audi TSB bookmarked. The whole point is to focus the actual bleeding process on the ABS pump and leverage it to force out air bubbles trapped inside the ABS pump, as well as the entire system.
You most definitely want to verify that vacuum hose connection (brake booster to engine vacuum line at firewall) is NOT involved, and on an early model car I'd definitely place a bet it is involved. I've had that one happen on my '10 already, temp fixed via duct tape, and when that began to relapse again, I redid it with JB Weld pipe repair tape to both seal it up tight and reinforce that connection point. If mine ever fails in future, then I'll cut out the bad section and insert some new fittings/hose, if the old booster vac hose is still good otherwise, which doesn't seem to be the issue; it's just the heat in engine bay that fatigues the thin plastic on the female connection side.
iv checked the vacuum pipe all seems to be ok on that front, but I’m curious on how air would get in int the first place. And how it’s only the front right wheel that’s locking up when I’m doing 60mph that’s what’s alarming and I can’t fix if I’m driving around town I have no issues at all it’s so bizzar
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Here's also an excellent thread outlining that this vacuum line issue is overlooked by both indie shops and of course, Audi dealers.
https://www.audiworld.com/forums/q7-...rakes-3040950/
https://www.audiworld.com/forums/q7-...rakes-3040950/
Thread Starter
AudiWorld Junior Member
Joined: May 2025
Posts: 34
Likes: 8
Here's also an excellent thread outlining that this vacuum line issue is overlooked by both indie shops and of course, Audi dealers.
https://www.audiworld.com/forums/q7-...rakes-3040950/
https://www.audiworld.com/forums/q7-...rakes-3040950/
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AudiWorld Super User
Joined: Jan 2021
Posts: 4,565
Likes: 1,456
From: USA - NM
appreciate the link there buddy was a interesting read while I have a very intermittent pedal issue my more pressing issue is the drivers front wheel just applying itself at highway speeds witch is more alarming and considering an vacuum leak to brake servo generally gives a hard pedal not a pedal just just drops to the floor once in a blue moon
Can't tell you how many threads like this there are where the OP says exactly the same thing you just did about the brake booster, which follows conventional wisdom if the brake booster is failed internally, and is also why the indie techs, DIY owners, and Audi 'Master Techs' fail to diagnose this issue and repair the car correctly the first time, then second time it comes back, then third time it comes back for same issue, etc. They just keep replacing expensive parts on your dime as they don't know what is wrong so they just keep swapping parts.
It literally takes two minutes under the hood to verify the vacuum leak issue exists, so I don't really understand the push-back on checking that out unless it's just too simple for you to understand that you haven't lost the full vacuum feed to the brake servo, and so it still works...most of the time, at least for now. The vacuum hose is what 'powers' the brake servo/booster, and your brake servo/booster is not the problem. It's the loss of vacuum pressure screwing with how it functions. I've been through this and resolved it for myself. I never would have suspected it being the vacuum line connection either, but it is what it is, and that connection leaks vacuum eventually and then slowly gets worse unless you repair that fitting to make it airtight again. Simple. Guarantee once you pull off the engine vac line from the booster's connect side you'll 100% understand the leak issue plain as day and then palm-slap your forehead in disgust. Wish I had a pic of mine, as it was split apart like flower petals.
Now on the brake caliper activation, my theory is that's just downstream symptomatic of a more basic underlying issue also, but in the ESC system, which is triggering that particular wheel caliper in response to input stimuli from something as inane as the height sensors, ABS/speed sensors, or yaw sensor. My money is that issue is sensor based. Low hanging fruit approach; you remove, clean, lube those height sensors articulation points, or at very least spray the joints down well with PB Blaster as a starting point...simple to visually check and spray down. Literally takes minutes of your time. The alternative (and Audi Stealer favorite); you replace the ABS controller and/or pump...two of the most expensive items in the system w/o verifying the simpler stuff that creates the signal used by the ESC system to determine what's happening with your car so the stability control can determine if it needs to intervene or not.
Here's a thought. Next time you go out on freeway, turn off your ESC (press the ESC button on dash next to emergency flashers button), and it'll give you a message that you in off-road mode, yada-yada on dash screen. Drive it and see what happens with that wheel caliper. A simple test, yah? In truth, it just reduces the sensitivity and trigger parameters greatly for the ESC system so the car can function well off-road and in slippery conditions or when wheels are off the ground due to terrain, etc., but it should give you a valid point of reference if that caliper doesn't activate, then you'll know it related to the ESC feedback loop rather than it being a 'ghost' in your ABS controller.
Honestly, what have you got to lose by doing simple validation checks?
That's all the wisdom I got for you on this matter. I do find it ironic though how mine started to act up again at brake pedal a year or so after my quicky DIY fix of the vacuum hoses, and so I just pulled off most of the 100mph tape and did the JB Weld tape over it carefully to make a permanent airtight seal, and it's right back to 100% throw me forwards against the seatbelt braking power again, as well as being able to modulate the brakes very finely through the pedal again. Now how could all that braking goodness be related to just a stupid little vacuum line connector leaking I wonder.
Good luck to you.
Hope you find your way back to braking normalcy soon.
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Thread Starter
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Yeah, you've got more than one issue there for sure with that one caliper activating 'by itself', which of course, it can't do...something has to trigger that brake circuit.
Can't tell you how many threads like this there are where the OP says exactly the same thing you just did about the brake booster, which follows conventional wisdom if the brake booster is failed internally, and is also why the indie techs, DIY owners, and Audi 'Master Techs' fail to diagnose this issue and repair the car correctly the first time, then second time it comes back, then third time it comes back for same issue, etc. They just keep replacing expensive parts on your dime as they don't know what is wrong so they just keep swapping parts.
It literally takes two minutes under the hood to verify the vacuum leak issue exists, so I don't really understand the push-back on checking that out unless it's just too simple for you to understand that you haven't lost the full vacuum feed to the brake servo, and so it still works...most of the time, at least for now. The vacuum hose is what 'powers' the brake servo/booster, and your brake servo/booster is not the problem. It's the loss of vacuum pressure screwing with how it functions. I've been through this and resolved it for myself. I never would have suspected it being the vacuum line connection either, but it is what it is, and that connection leaks vacuum eventually and then slowly gets worse unless you repair that fitting to make it airtight again. Simple. Guarantee once you pull off the engine vac line from the booster's connect side you'll 100% understand the leak issue plain as day and then palm-slap your forehead in disgust. Wish I had a pic of mine, as it was split apart like flower petals.
Now on the brake caliper activation, my theory is that's just downstream symptomatic of a more basic underlying issue also, but in the ESC system, which is triggering that particular wheel caliper in response to input stimuli from something as inane as the height sensors, ABS/speed sensors, or yaw sensor. My money is that issue is sensor based. Low hanging fruit approach; you remove, clean, lube those height sensors articulation points, or at very least spray the joints down well with PB Blaster as a starting point...simple to visually check and spray down. Literally takes minutes of your time. The alternative (and Audi Stealer favorite); you replace the ABS controller and/or pump...two of the most expensive items in the system w/o verifying the simpler stuff that creates the signal used by the ESC system to determine what's happening with your car so the stability control can determine if it needs to intervene or not.
Here's a thought. Next time you go out on freeway, turn off your ESC (press the ESC button on dash next to emergency flashers button), and it'll give you a message that you in off-road mode, yada-yada on dash screen. Drive it and see what happens with that wheel caliper. A simple test, yah? In truth, it just reduces the sensitivity and trigger parameters greatly for the ESC system so the car can function well off-road and in slippery conditions or when wheels are off the ground due to terrain, etc., but it should give you a valid point of reference if that caliper doesn't activate, then you'll know it related to the ESC feedback loop rather than it being a 'ghost' in your ABS controller.
Honestly, what have you got to lose by doing simple validation checks?
That's all the wisdom I got for you on this matter. I do find it ironic though how mine started to act up again at brake pedal a year or so after my quicky DIY fix of the vacuum hoses, and so I just pulled off most of the 100mph tape and did the JB Weld tape over it carefully to make a permanent airtight seal, and it's right back to 100% throw me forwards against the seatbelt braking power again, as well as being able to modulate the brakes very finely through the pedal again. Now how could all that braking goodness be related to just a stupid little vacuum line connector leaking I wonder.
Good luck to you.
Hope you find your way back to braking normalcy soon.
Can't tell you how many threads like this there are where the OP says exactly the same thing you just did about the brake booster, which follows conventional wisdom if the brake booster is failed internally, and is also why the indie techs, DIY owners, and Audi 'Master Techs' fail to diagnose this issue and repair the car correctly the first time, then second time it comes back, then third time it comes back for same issue, etc. They just keep replacing expensive parts on your dime as they don't know what is wrong so they just keep swapping parts.
It literally takes two minutes under the hood to verify the vacuum leak issue exists, so I don't really understand the push-back on checking that out unless it's just too simple for you to understand that you haven't lost the full vacuum feed to the brake servo, and so it still works...most of the time, at least for now. The vacuum hose is what 'powers' the brake servo/booster, and your brake servo/booster is not the problem. It's the loss of vacuum pressure screwing with how it functions. I've been through this and resolved it for myself. I never would have suspected it being the vacuum line connection either, but it is what it is, and that connection leaks vacuum eventually and then slowly gets worse unless you repair that fitting to make it airtight again. Simple. Guarantee once you pull off the engine vac line from the booster's connect side you'll 100% understand the leak issue plain as day and then palm-slap your forehead in disgust. Wish I had a pic of mine, as it was split apart like flower petals.
Now on the brake caliper activation, my theory is that's just downstream symptomatic of a more basic underlying issue also, but in the ESC system, which is triggering that particular wheel caliper in response to input stimuli from something as inane as the height sensors, ABS/speed sensors, or yaw sensor. My money is that issue is sensor based. Low hanging fruit approach; you remove, clean, lube those height sensors articulation points, or at very least spray the joints down well with PB Blaster as a starting point...simple to visually check and spray down. Literally takes minutes of your time. The alternative (and Audi Stealer favorite); you replace the ABS controller and/or pump...two of the most expensive items in the system w/o verifying the simpler stuff that creates the signal used by the ESC system to determine what's happening with your car so the stability control can determine if it needs to intervene or not.
Here's a thought. Next time you go out on freeway, turn off your ESC (press the ESC button on dash next to emergency flashers button), and it'll give you a message that you in off-road mode, yada-yada on dash screen. Drive it and see what happens with that wheel caliper. A simple test, yah? In truth, it just reduces the sensitivity and trigger parameters greatly for the ESC system so the car can function well off-road and in slippery conditions or when wheels are off the ground due to terrain, etc., but it should give you a valid point of reference if that caliper doesn't activate, then you'll know it related to the ESC feedback loop rather than it being a 'ghost' in your ABS controller.
Honestly, what have you got to lose by doing simple validation checks?
That's all the wisdom I got for you on this matter. I do find it ironic though how mine started to act up again at brake pedal a year or so after my quicky DIY fix of the vacuum hoses, and so I just pulled off most of the 100mph tape and did the JB Weld tape over it carefully to make a permanent airtight seal, and it's right back to 100% throw me forwards against the seatbelt braking power again, as well as being able to modulate the brakes very finely through the pedal again. Now how could all that braking goodness be related to just a stupid little vacuum line connector leaking I wonder.
Good luck to you.
Hope you find your way back to braking normalcy soon.
AudiWorld Super User
Joined: Jan 2021
Posts: 4,565
Likes: 1,456
From: USA - NM
ESC = Electronic Stability Control
It works by using sensor data to understand what's happening to the car dynamically. It uses the data from multiple different sensors (ABS /speed, height, yaw sensor, etc., etc),and then applies the brakes as required, both selectively and automatically using the high pressure loop of the ABS module to 'correct' for the perceived peril it interprets from the data it has to work with. When it activates there will be indicator lights lit or flashing on the dash for ESC/ABS during the event, etc. All of this matches your description to the letter of the caliper activating, lights on dash, ABS pump getting after it strongly, etc., etc.
On the vacuum line leak; you absolutely just confirmed what I've been saying to you, you just can't see it yet. You broke the vacuum pump pipe, so the lack of vacuum caused hard pedal at the booster/brake servo even while car is running. Yeah, exactly...the brake booster works off of vacuum pressure. It's still getting vacuum pressure, but the leaky connection in the brake booster line is causing it to exist in that area between full-on booster failure (zero assist) and normal braking operation...soft/spongy pedal, and occasionally it goes down to floor with basically no braking support provided, etc. Been there, done that, fixed it with JB Weld tape. Buy the new vacuum hose and install that if you want to spend some money on parts. I didn't see the point in that as it's just the connector to engine vacuum side that's leaking, which can be easily resolved by removing the 'bad' section and patching back together, or depending on the condition, perhaps JB Weld pipe repair tape would suffice, as in my case.
Have a nice day!
I believe it was Will Rogers that famously said "You can lead a horse to water, but you can't make him drink".
It works by using sensor data to understand what's happening to the car dynamically. It uses the data from multiple different sensors (ABS /speed, height, yaw sensor, etc., etc),and then applies the brakes as required, both selectively and automatically using the high pressure loop of the ABS module to 'correct' for the perceived peril it interprets from the data it has to work with. When it activates there will be indicator lights lit or flashing on the dash for ESC/ABS during the event, etc. All of this matches your description to the letter of the caliper activating, lights on dash, ABS pump getting after it strongly, etc., etc.
On the vacuum line leak; you absolutely just confirmed what I've been saying to you, you just can't see it yet. You broke the vacuum pump pipe, so the lack of vacuum caused hard pedal at the booster/brake servo even while car is running. Yeah, exactly...the brake booster works off of vacuum pressure. It's still getting vacuum pressure, but the leaky connection in the brake booster line is causing it to exist in that area between full-on booster failure (zero assist) and normal braking operation...soft/spongy pedal, and occasionally it goes down to floor with basically no braking support provided, etc. Been there, done that, fixed it with JB Weld tape. Buy the new vacuum hose and install that if you want to spend some money on parts. I didn't see the point in that as it's just the connector to engine vacuum side that's leaking, which can be easily resolved by removing the 'bad' section and patching back together, or depending on the condition, perhaps JB Weld pipe repair tape would suffice, as in my case.
Have a nice day!
I believe it was Will Rogers that famously said "You can lead a horse to water, but you can't make him drink".
Last edited by '10Q7TDI_Prestige'; Jun 9, 2025 at 10:52 AM.