Sport Diff failure? Nothing more than a spurious warning light, it turns out. The car went back to Audi, who tested it and found nothing awry. The warning was reset and the car was faultless for the remainder of its time with us.
Le Mans was the final big journey for the S4, one that should have played to its strengths of performance and practicality. For the most part it was very good, as well: you really appreciate how nice the interior is after many hours there, it's impeccably refined and the stereo/nav combination is excellent.
A few little issues did become apparent over the weekend though. First being that, well, it's not all that big in the back. The door aperture is a bit narrow for the rear and the boot only seemed adequate for what we needed rather than truly commodious. I know that tends to be the way with compact exec estates, but it's obviously far more apparent when you actually come to test it.
That didn't stop the S4 being an entirely pleasant and quite enjoyable car to cover any kind of journey in. Perhaps you could accuse it of lacking a bit of edge, though an ex-owner (of the V8 car) that I know put it well when he said, "I think the problem with the 'S' sub-brand is that people expect it to be a more affordable RS, whereas it's actually more of a hot tourer." Which is exactly the role the S4 fulfils, with tidier handling than you probably expect too.
And if you do want an RS? Well there's plenty to be encouraged by with the RS5, even if there's a lot that we have to hope doesn't make the cut too. The engine is more exciting, the gearbox improved and, well, imagine how good the RS4 could look in Sonoma Green. Sort the RS5's ride out while keeping all that is good about the S4 (and there is plenty) and the potential is there for a great fast estate.
Car: 2016 Audi S4 Avant
On fleet since: January 2017
List price new: £44,415 (As tested £49,770 comprising Misano Red paint for £645, Quattro sport with Sport Differential for £1,200, 19-inch diamond cut wheels for £550, Light and Vision pack for £750, Adaptive S Sport suspension with damping control for £900, Audi phonebox with wireless charging for £325 and on the road costs of £985)
Last month at a glance: Auf wiedersehen to the Audi Avant - bring on the RS4!
Audi S4 arrives on the fleet
Audi S4: Review
Getting to grips with another AWD Avant
Hang on, an Audi with appeal beyond just the showroom?
What's the square route of S4?
Is the Sport Diff duff?