The brief
Mr Lim's A5 was towed in after it had stalled and started bellowing white smoke. White smoke and a stall sounds alarming, but the cause here wasn't a worn-out engine, it was something simpler that had been quietly causing trouble. Audi reads the oil level electronically with a sensor in the sump and shows it on the dash. When that sensor fails it reports a level that isn't real, and if it keeps saying the oil is low, the driver tops up, again and again, until the engine is overfilled. Too much oil gets whipped into foam, the crankcase pressure rises, oil pushes past seals and into the cylinders, and you get white smoke and rough running or a stall. The fix is to drain the excess down to the correct level and replace the faulty sensor so it reads true.
The diagnosis
On the lift the 360-degree check ruled out other causes, and the picture was clear: the oil level sensor was faulty, sending false low readings, so the engine had been over-dosed with oil from repeated top-ups, and the overfill is what caused the white smoke and the stall. The engine itself was sound. That's a new oil level sensor plus draining the oil back to the correct level, rather than tearing into an engine that the wrong sensor and an overfill had made look worse than it was.
The work
The excess oil was drained out and the level set to the correct mark. The faulty oil level sensor was removed and a new genuine Audi-spec sensor fitted with a fresh seal, the fault cleared, and the system checked, the dash now reading OIL LEVEL OK accurately. The engine was run and checked. A road test confirmed a clean start with no smoke, smooth running, the dash reading the correct level, and no warning lights.
The outcome
No white smoke, a clean start, smooth running, the dash reading the correct oil level, and no warning lights, on an engine that was never the problem. Mr Lim got the A5 back running properly. The lesson is not to ignore or chase an oil warning by just topping up, get it checked, because a faulty sensor and an overfill can look a lot worse than they are, and outside a thirsty V8 or V10 it's not normal for an engine to keep wanting oil.
