Owner's Problem Description
The owner reports that both the auxiliary and condenser fans stopped working four days after the auxiliary fan was replaced. They have replaced the Engine Coolant Temperature (ECT) sensor and the fan switch, and checked the standard fuses near the driver's door. Despite these efforts, the fans remain non-functional.
Professional Technical Analysis
The 2001 Audi A6 is equipped with a 2.7L V6 engine and has approximately 120,000 miles on the odometer. The reported issue involves both the auxiliary and condenser fans failing to operate, which can lead to overheating and subsequent engine damage if not addressed promptly. This problem arose shortly after the auxiliary fan replacement, indicating a potential fault in the cooling system's electronic controls or wiring. The auxiliary fan and condenser fan circuits are interconnected through the coolant fan control module, which regulates fan operation based on inputs from the ECT sensor and other cooling system parameters. Given that the ECT sensor was replaced, it is crucial to confirm that the sensor is providing accurate data to the Engine Control Module (ECM). A malfunctioning fan control module is also a common failure point in this model, especially if it was subjected to moisture or heat damage. The owner has verified that all relevant fuses are operational, which suggests that the issue is likely not fuse-related but may involve a wiring fault or a failure in the control module itself. The current condition of the vehicle poses a safety concern due to the risk of overheating, and further diagnostics should focus on the control module and associated wiring. A proper diagnosis should include checking the operation of the after-run thermal switch, which is critical for fan operation after the engine is turned off.
Possible Causes
Most common causes (ordered by frequency):
- Coolant Fan Control Module Failure: The control module may have failed due to internal components degrading over time or exposure to moisture, affecting its ability to control both the auxiliary and condenser fans. The module is responsible for receiving signals from the ECT sensor and activating the fans accordingly. Testing should confirm that the module is receiving voltage and outputting signals as expected. Typical symptoms of a failing module include intermittent operation or complete failure of fan activation. - Non-responsive fans after module replacement, consistent voltage readings at the module input but no output signals detected at the fan connectors.
- Wiring Issues: Damaged or corroded wiring between the control module and the fan motors can prevent signal transmission necessary for fan operation. Visual inspection and continuity testing of the wiring harness are essential to identify any faults. Corrosion at connectors can lead to high resistance, causing voltage drops that may prevent the fans from engaging. - Visual inspection reveals frayed insulation, resistance checks show inconsistent readings in wiring continuity, and corroded connectors.
- After-Run Thermal Switch Failure: This switch is designed to ground the fan motors when the engine is turned off, allowing the fans to run to cool down the engine. If this switch fails, it could prevent the fans from operating even when required. Testing the after-run thermal switch for continuity and functionality is critical, especially after the engine has been turned off. - Fans fail to operate after engine shutdown, resistance checks show open circuit on the thermal switch.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial OBD-II Scan: Use GeekOBD APP to perform an initial diagnostic scan of the vehicle's OBD-II system. Check for any stored fault codes related to the cooling system and monitor live data related to the engine temperature and fan operation. This step helps identify any electronic issues that may be affecting the fans.
- STEP 2 - Voltage Testing at Control Module: Use a multimeter to check the voltage at the input and output terminals of the coolant fan control module. Input should read battery voltage (12-14V), and output should activate when the engine reaches operating temperature. If input is present but output is missing, the control module may need replacement.
- STEP 3 - Wiring Inspection: Conduct a thorough visual inspection of the wiring harness and connectors from the control module to the fans. Look for signs of wear, corrosion, or damage. Continuity testing with a multimeter should confirm that there are no breaks in the wiring that could impede signal transmission.
- STEP 4 - After-Run Thermal Switch Testing: Test the after-run thermal switch for continuity and functionality. This is crucial for ensuring that the fans can operate after the engine is turned off. If the switch is found to be faulty, it should be replaced.
