The brief
Mr Pua's Q5 came in with two things: an intermittent warning saying the engine oil was low, and an unusual noise from the brakes. So two jobs in one visit, the false alarm and the brake noise, and both got looked at properly rather than guessed at. An oil warning is never one to wave off, low oil pressure destroys an engine fast, so the first job is to confirm whether the oil is really low or the car is misreading it. The oil pressure switch is the sender that tells the dash what the pressure is, and it sits in hot oil for years until it fails and reports a pressure that isn't real, lighting the warning on a healthy engine. The brake noise, meanwhile, is the rear pads telling you they're due, and once they hit the wear line they get changed.
The diagnosis
We checked the actual oil level and pressure first, both fine, healthy, no leak. The Audi diagnostic handset showed the oil pressure switch was the fault, reading wrong, which is the intermittent warning. At the back, the rear brake pads were worn, which is the disturbing sound. The rest of the car was sound. So it was an oil pressure switch replacement plus rear brake pads, the false alarm fixed and the brake noise eliminated.
The work
The faulty oil pressure switch was removed and a new genuine Audi-spec switch fitted with a fresh seal, the fault cleared and the system checked to be reading the pressure correctly. At the rear, the worn pads were removed, the calipers cleaned and the slides freed, and new genuine Audi-spec rear pads fitted, the discs checked, every fastener torqued to the manual figures and the brakes bedded in. A road test confirmed no oil warning, the pressure reading correctly, and the rear brakes pulling up firm, even and quiet.
The outcome
No low-oil warning, the pressure reading correctly on a healthy engine, and the rear brakes firm, even and quiet. Mr Pua got the Q5 back with the false alarm and the brake noise both sorted. Checking the oil before swapping the switch meant we fixed the actual fault rather than an engine that didn't have one, and doing the rear pads dealt with the noise.
