P0128 (Audi): Defective Engine Thermostat, Defective Engine Coolant Temperature… — what it means, the affected system and what to check before replacing parts.
Defective Engine Thermostat, Defective Engine Coolant Temperature Sensor, Defective Intake Air Temperature Sensor, Defective Cooling System, Low Engine Coolant, Dirty Engine Coolant causing incorrect Coolant Temperature Sensor readings, Defective/always running Engine Cooling fan(s). Source catalogue definition; confirm applicability using vehicle service information.
Affected system: Powertrain