While the 2003 Audi A4’s cooling fan control module (J293) doesn’t communicate directly with VCDS Lite, you can still diagnose potential issues. This module, located above the electric fan, relies on a pulsed-width-modulated (PWM) signal from the Engine Control Module (ECM – J220) to activate the fan. VCDS Lite can be used to indirectly determine if the compressor is engaging by monitoring the ECM’s commands to the cooling fan, which often runs in conjunction with the AC compressor.
Diagnosing the Cooling Fan Circuit with VCDS Lite
To check if the ECM is signaling the fan, perform an Output Test using VCDS Lite with the key on and engine off. The fan should gradually increase to 100% speed and then return to 0%. This test utilizes the ECM’s control over the fan, indirectly indicating potential compressor activity as the compressor often triggers the fan.
Furthermore, monitor Measuring Value Block (MVB) Group 135, Field 2 in VCDS Lite. This displays the current fan speed output (%) from the ECM. A reading other than 0% while the AC is on suggests the ECM is commanding the fan, and by extension, likely the compressor. Additionally, MVB 137 provides insights into the AC system’s status and requests, potentially offering further clues about compressor operation.
Further Troubleshooting if the Fan Doesn’t Operate
If the Output Test fails and MVB 135 shows 0%, inspect fuses S4 (5A) on the left side of the dash and S42 (40/60A) above the relay panel. If the fuses are intact, verify the PWM signal from the ECM to the J293 using an oscilloscope. While a DVOM set to AC voltage might detect some voltage (RMS), an oscilloscope provides a more accurate reading.
Absence of an ECM signal necessitates checking the red/white wire connecting the ECM to the J293. If voltage and signal reach the J293 but the fan remains inactive, the J293 module itself may be faulty. Remember, while these steps focus on the cooling fan, they provide valuable indirect evidence of the compressor’s operational status due to their interconnected nature within the AC system. A properly functioning fan, responding to ECM commands, often signifies a working compressor.
