Here’s a great candidate for a check-up at an Audi dealer ahead of your purchase, if you’re not set on buying one from a Certified Pre-Owned program at a dealer, which will include a full inspection of the car before your purchase.

Have an Audi mechanic inspect the water pump and cooling system for signs of leakage, or indications of imminent water-pump failure, which may include warning messages in the instrument cluster, or signs of leakage or spraying of coolant from the water pump. The S4’s water pump is made of plastic, which many owners figure is a bad idea because it’s a water pump. Replacement water pump units are made of aluminum, which is metal, which is likely better suited to the application. More reading here and here.

Note that leaky thermostats were also reported in discussions of S4 coolant leaks, though the owner’s community suggests that these issues only affected earlier models, and had been addressed by Audi by about 2012. A mechanic should check for an unlikely but possible fluid leak from the rear differential, too. If one is noted, a bad seal or seals may be the culprit.

From 2013, a new power-steering system was used in the S4, with mixed reactions from the owner’s community. More reading here and here. This looks like another case of a new-car electric power steering system being tuned and calibrated in a way that doesn’t feel natural to drivers, though some owners have reported what feels like a slipping or disconnected feeling from the steering at speed, for a few seconds, and the sensation of ‘drifting’ down their lane with a loose or numb steering wheel. Some owners have had new steering system software installed to correct the issue. This isn’t an Audi-specific issue, and has been reported by owners of various vehicles.

Further, note that earlier models may suffer from a wobble or shudder in the steering in tight, low-speed cornering situations. If this is apparent on a test-drive, have an Audi mechanic inspect the front-end of the S4 you’re considering, but be aware that in many cases, this is diagnosed as a natural and inherent characteristic of the car.

If you’re set on a model with the Direct Shift Gearbox (DSG) dual-clutch transmission, drive it with an eye for shift quality and consistency. This gearbox should shift at lightning speed with perfect rev-matching and absolute smoothness to gear changes in both directions. If that’s not the case, or any clumsiness or hard shifting is detected, be sure to have an Audi technician investigate. Typically, issues like these are addressed by reprogramming the computer that controls the DSG transmission, and aren’t related to the transmission itself – though be sure that’s the case if any issues are noted.

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