A “Check Coolant Level” warning on your dashboard can be perplexing, especially when there’s no apparent leak and the system has passed a pressure test. This article delves into such a scenario encountered in an Audi S4, using VCDS (Vag-Com Diagnostic System) to diagnose the issue and focusing on understanding the comfort coolant pressure system. The fault stubbornly reappeared after short drives, requiring a VCDS reset each time. Replacing the coolant bottle didn’t resolve the issue, as it was discovered the bottle itself doesn’t house a sensor, but rather two electrical contacts that signal coolant presence. This points to the sensor likely being integrated within the ECU.
Decoding the “Unknown Error Code”
Despite normal operating temperatures and consistent coolant levels, VCDS reported a fault in Address 01: Engine as “33688 – ROD – Unknown Error Code.” This cryptic message often indicates a problem with the ROD (Repair Order Data) file or a compatibility issue between VCDS and the vehicle’s ECU. In this case, the user confirmed using the latest VCDS version and a new cable, ruling out those possibilities. The full VCDS scan is provided below.
VCDS Comfort Coolant Pressure: Potential Culprits
While the “Unknown Error Code” doesn’t pinpoint the exact problem, it necessitates a deeper dive into potential causes related to comfort coolant pressure. Here are some possibilities:
- Faulty Coolant Level Sensor within the ECU: Though the coolant bottle itself doesn’t contain a traditional sensor, the ECU likely monitors coolant pressure and level. A malfunctioning sensor within the ECU could trigger the fault despite normal coolant levels.
- Wiring Harness Issue: Damaged or corroded wiring in the coolant level sensor circuit could disrupt signal transmission, leading to a false positive.
- ECU Software Glitch: A software bug within the engine control unit might be misinterpreting data, triggering the erroneous fault code. A software update might be necessary.
- Grounding Problem: A poor ground connection in the sensor circuit can interfere with signal accuracy, potentially triggering the fault.
Next Steps in Diagnosis
To further investigate the persistent “Check Coolant Level” fault and the enigmatic “33688” code, consider these steps:
- Consult Ross-Tech: As the developers of VCDS, Ross-Tech possesses in-depth knowledge of the software and potential compatibility issues. They might offer insights into the “Unknown Error Code” and suggest targeted diagnostic procedures.
- Check for Technical Service Bulletins (TSBs): Audi may have issued TSBs addressing similar issues in other S4 models. These bulletins provide official guidance on diagnosis and repair.
- Live Data Analysis with VCDS: Monitoring coolant pressure related live data parameters using VCDS while driving could reveal anomalies that pinpoint the problem source.
Conclusion: Unraveling the Mystery
Diagnosing intermittent faults like this requires a systematic approach. While the “Unknown Error Code” initially hinders diagnosis, focusing on the comfort coolant pressure system and utilizing available resources like Ross-Tech and TSBs can lead to a solution. Further investigation with VCDS, especially live data analysis, is crucial to uncovering the root cause and resolving the persistent “Check Coolant Level” warning.
Thursday,19,May,2022,17:14:23:65343 VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64 VCDS Version 22.3.1.4 (x64) HEX-V2 CB: 0.4615.4 Data version: 20220407 DS337.0 www.Ross-Tech.com VIN: ******************* License Plate: Mileage: 78386km-48706mi Repair Order: ... (Full VCDS Log as in original post) ...