Thesecond-worst-rated problem for Audi A4 by Car Complaints is engine failure, which earns a severity rating of 10.0 with an average repair cost of $6,500 and an average mileage of around 66,000 miles. A bad piston is extremely costly and earns a severity rating of 10.0, with an average cost of around $8,500 to fix. TheS4 meanwhile, comes with a 3.0L turbocharged V6 making 349 horsepower and 369 lb-ft of torque. The gearbox is also different, as the S4 sends power to all-four wheels via an 8-speed automatic FpLxsx.