The Audi B7 (2005-2008) 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 or even a full VCDS system. However, you can still use VCDS Lite to indirectly diagnose potential cooling fan problems.
The Engine Control Module (ECM), labeled J220, commands the J293 to activate the fan. It achieves this by sending a Pulse Width Modulated (PWM) signal via a dedicated wire to the J293. This signal instructs the fan on how fast to spin.
Using VCDS Lite, you can perform an Output Test on the ECM with the key on and the engine off. This test should cause the fan to gradually increase speed from 0% to 100% and then return to 0%. Observe the fan’s behavior during this test.
If the fan doesn’t respond, check Measuring Value Block (MVB) Group 135, Field 2 within VCDS Lite. This field displays the ECM’s commanded fan speed as a percentage. Additionally, MVB Group 137 provides insights into the AC system’s status and requests, which can influence fan operation. !(MVB 135 in VCDS)[https://forums.ross-tech.com/index.php?attachments/upload_2023-9-14_11-14-32-png.11871/]
Should these checks appear normal, inspect fuses S4 (5A) located on the left side of the dash and S42 (40/60A) positioned above the relay panel in the dash.
If the fuses are intact, investigate the signal from the ECM to the J293. An oscilloscope is the ideal tool for this task, allowing you to visualize the PWM signal. While a Digital Volt-Ohm Meter (DVOM) set to AC voltage might show a voltage reading, this only represents the Root Mean Square (RMS) voltage and doesn’t provide a complete picture of the signal. ![Oscilloscope reading of PWM signal][https://www.electroschematics.com/wp-content/uploads/2011/04/pwm-signal.gif]
If no signal is detected from the ECM, 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 unresponsive, the J293 module itself is likely faulty. In this scenario, replacement of the J293 module is typically necessary. Using VCDS Lite in conjunction with these diagnostic steps can help pinpoint the root cause of cooling fan issues in your Audi B7.
