A4Alan

My A4 Allroad has a similar issue. My local Audi dealer changed the drop link under warranty thinking it would fix it but it didn't. Closer inspection revealed that brake pad retaining clips were missing and it was the pads that were loose. Get under the car and give the brakes a good check out.

I've been through the mill with my 2017 A4 Allroad on this. My advice is get it fixed as soon as Brake Servo Restricted error message appears. £70 for the brake pressure sensor and 10 mins max to replac. Audi Roadside Assistance who came to my aid when message changed to Brake Failure - do not drive said there was no clear reason why this is happening but best case scenario is new brake pressure sensor @ £70, worst case in new ABS unit @ £2600. I was worst case but thankfully was cover buyAudi Approved Used warranty. Car has been off the road for 2 weeks though getting it fixed. Around about the time the error message changed I bought a new sensor from Autodoc but it turned out I didn't need as the technician had his own supply on the van. I have a brand new brake sensor for sale if anybody wants to get in touch and buy it - never been fitted. £60 inc postage.