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A few days ago, as soon as I started the Q7, a warning message appeared which I've never seen before: Brake booster: Limited functionality. You can continue driving. Please contact service. When driving, the brakes still functioned but the baking feel was not as smooth and there was a faint humming when the car was about to come to a full stop. There was another warning that start-stop was no longer operational and that the traffic assist was no longer operational (in fact, the cruise control function was inoperative but lane assist still worked). I scheduled a dealer service appointment for tomorrow, and couldn't find anyting describing the issue on the forum. One thing that stands out is that I've used the traffic assist for the first time before the warning message appearing - having never used this function prior to this. Other than this, everything seems to be working fine.
The only thing I found when seaching on this issue is this: https://www.dash-lights.com/audi/a5-...arning-lights/ Warning message: Brake booster: Limited functionality. You can continue driving. Please contact service. This indicates a malfunction in the brake booster. The brake booster increases braking force in order to increase braking and stopping ability. In this instance, you can continue to drive carefully. The brake booster is still functioning but at reduced effectiveness
I had that and it was traced to a battery that was dying and couldn't take a charge. New battery fixed the issues.
Thank you, this sounds like it could be my issue as well as I don't drive the Q7 enough and the batteries don't like that. The fact that start-stop isn't working seems consistent with AGM battery problems as well. I am at the dealership now and mentioned the above to the service techs.
Update: according to the dealer tech, it seems to be a faulty pressure sensor, although it wasn't specified to me which one. Not in stock and will take a day or two to arrive, so a loaner... Will see if it fixes the problem and what it was when I get the report
Last edited by dohturdima; 09-08-2020 at 10:39 AM.
Just heard back from the dealer: it was a brake booster sensor (they stated G608 but I haven't found it in the parts list for our cars so think it is actually this one). They told me that they needed to perform an alignment afterwards. Out of warranty, I am pretty sure it would have been a pretty costly repair.
Reviving this thread as the dreaded message popped up again, less than 3 years later. I immediately stopped driving, as read online that despite the message that driving is permitted - that would shift tthe stopping load to the ABS sensor and wipe it out in a matter of a week (which would cost $$$ to repair/replace).. Decided to swap out the Pressure sensor (Audi Part #5Q0-906-207-B) whcih I will buy a local dealer and try to wipe the message with ODBII - will report back. Scheduled a dealer appointment just in case.
Turned out that rats chewed through the wires connected to the booster sensor. Dealer didn't spot it the first time and just swapped out the sensor, or the damage was done later / in any case, effin NYC. Had a local shop resolder the wires, the sensor was fine, good to go.
Well I wish I had found this thread earlier, I have been driving my 18 Q7 with this brake booster warning for 3 months now because the dealer could only sechedule me 3 months later. Now a day before my scheduled appointment the Brake booster warning turned to a Brake malfunction and had to get the car towed. The dealer changed the vacuum sensor it helped remove some errors but now I have a bad ABS module and of course its a very expensive replacement cost.
Turned out that rats chewed through the wires connected to the booster sensor. The dealer didn't spot it the first time and just swapped out the sensor, or the damage was done later / in any case, effin NYC. Had a local shop resolder the wires, the sensor was fine, good to go.
I received the same error last week. Searched the error and found this thread before even popping my hood. Looked under the master cylinder and it was full of leaves and insulation. Mouse made a nest and chewed something. Do you know where it had chewed the cable? I really dont want to pay shop rate to have them trace it all down.
I received the same error last week. Searched the error and found this thread before even popping my hood. Looked under the master cylinder and it was full of leaves and insulation. Mouse made a nest and chewed something. Do you know where it had chewed the cable? I really dont want to pay shop rate to have them trace it all down.
Sorry, just noticed this post. I will try to take a Pic later on today and upload.
09-07-2020, 08:24 AM
Brake booster warning
