The 2003 Audi A4 B7 utilizes a J293 Coolant Fan Control (FC) module to manage the electric cooling fan. This module, positioned above the fan itself, lacks diagnostic capabilities and doesn’t communicate with VCDS Lite. However, understanding the system and using VCDS Lite for indirect diagnosis can help pinpoint issues.
While the J293 module doesn’t interact directly with VCDS Lite, the Engine Control Module (ECM), designated as J220, does. The ECM commands the fan operation via a Pulse Width Modulated (PWM) signal sent to the J293 through a dedicated wire. This connection allows for indirect diagnosis using VCDS Lite.
An Output Test performed on the ECM with the ignition on and the engine off can provide valuable insights. During this test, observe the cooling fan; it should gradually increase speed from 0% to 100% and then return to 0%. This test utilizes VCDS Lite’s functionality to activate the ECM’s fan control output, helping determine if the signal is being sent correctly.
If the fan doesn’t respond during the Output Test, VCDS Lite can be used to check specific Measuring Value Blocks (MVBs). MVB Group 135, Field 2 displays the current fan speed output from the ECM as a percentage. Additionally, MVB Group 137 provides information on the AC system’s status and requests, potentially revealing related issues that might affect fan operation. These readings within VCDS Lite offer crucial data for troubleshooting.
Should the VCDS Lite readings appear normal, further investigation is required. Check fuses S4 (5 amp) located on the left side of the dash and S42 (40/60 amp) above the relay panel. If the fuses are intact, the signal from the ECM to the J293 needs to be examined. While an oscilloscope is the ideal tool for analyzing the PWM signal, a digital voltmeter (DVM) set to AC voltage can provide a basic voltage reading (RMS).
Absence of an ECM signal points towards a potential wiring problem between the ECM and the J293. The red/white wire carries this signal and should be inspected for damage or disconnection. If voltage is present at the J293 and the fan still doesn’t operate, the J293 module itself is likely faulty.
In conclusion, while the Audi A4 B7’s J293 module doesn’t directly communicate with VCDS Lite, the software allows for indirect diagnosis through interaction with the ECM. By utilizing VCDS Lite’s Output Test function and examining relevant MVBs, along with traditional troubleshooting methods, the root cause of cooling fan issues can be effectively identified.
