The 2003 Audi A4 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. Therefore, accessing live data for the fan relay directly through VCDS is not possible. However, you can still diagnose potential issues using VCDS and other methods.
This article outlines how to troubleshoot your A4’s cooling fan using indirect VCDS data and other diagnostic techniques. Since the Engine Control Module (ECM), labeled J220, commands the fan via a Pulse Width Modulated (PWM) signal, we can leverage the ECM’s VCDS data for diagnosis.
A wiring diagram reveals the connection between the ECM (J220) and the J293 fan control module. This red/white wire carries the PWM signal from the ECM to command the fan’s operation. Using VCDS, you can perform an Output Test on the ECM with the key on and engine off. During this test, the fan should gradually increase speed from 0% to 100% and then return to 0%.
If the fan doesn’t respond during the Output Test, further investigation is necessary. Check Measuring Value Block (MVB) Group 135, Field 2 within VCDS. This field displays the current fan speed output command from the ECM as a percentage. Additionally, MVB Group 137 provides insights into the AC system’s status and requests, which can influence fan operation.
If the VCDS data appears normal, inspect fuses S4 (5 amp) on the left side of the dash and S42 (40/60 amp) above the relay panel. If the fuses are intact, you’ll need to verify the signal from the ECM to the J293. An oscilloscope is the ideal tool for this task, allowing you to visualize the PWM signal. A DVOM set to AC voltage can potentially detect voltage, but this only represents the Root Mean Square (RMS) voltage.
Should the ECM signal be absent, meticulously examine the wiring between the ECM and the J293, specifically the red/white wire. If voltage and signal are present at the J293, but the fan remains inoperative, the J293 module itself is likely faulty. By systematically investigating these areas, you can pinpoint the root cause of your Audi A4’s cooling fan malfunction.
