2007 Audi S4 B7 with P0698 Code: Spark Plug Light and Climate/Throttle Failure
I own a 2007 Audi S4 B7 and am experiencing a recurring issue. When I start the car, the engine runs normally and I can drive any distance. However, after stopping and restarting the vehicle, the spark plug warning light and engine temperature warning (yellow) illuminate. Once these lights turn off, the climate control system stops working entirely, and the accelerator pedal becomes unresponsive—the engine remains at idle. A diagnostic test reveals a sensor reference error: 'Sensor C Error Reference Error' with fault code P0698. This issue has not been resolved by standard troubleshooting. Has anyone else encountered this problem on their 2007 Audi S4 B7? What is the recommended course of action?
The P0698 code indicates a low reference voltage in Sensor C, which may point to an issue with the Engine Control Module (ECM). According to Audi's official trouble tree, this fault is often resolved by replacing the ECM—though no further testing or explanation is provided. It is recommended to consult an authorized Audi service center before proceeding with replacement, as this code can be sensitive and requires proper diagnostics.