A 2019 VW Caddy recently presented with a perplexing issue: a “Databus Implausible Message” fault code (U1122) within the engine control unit (ECU). Despite the error, the engine ran without noticeable performance issues. However, the driver assistance systems, including cruise control, malfunctioned. This article delves into the diagnostics and potential solutions for this specific scenario.
Understanding the “Databus Implausible Message” in VCDS
The U1122 fault code, often described as “Databus Implausible Message,” indicates a communication breakdown within the vehicle’s network. The various control modules in a modern car communicate with each other over a network called a databus. This allows them to share critical information and coordinate functions. An implausible message suggests that one module has sent data that another module deems illogical or inconsistent.
In this VW Caddy case, the VCDS scan revealed the U1122 fault originating from the engine control module (Address 01). While the engine itself functioned correctly, the fault impacted dependent systems like driver assistance and cruise control. This highlights the interconnected nature of modern vehicle systems. A seemingly isolated fault in one module can have cascading effects on others.
Diagnosing the Root Cause of U1122
The VCDS scan provided valuable information:
- Fault Code: 17923 – Databus U1122 00 [00100111] – Implausible Message
- Module: 01-Engine (J623-DFSD)
- Freeze Frame Data: Captured vehicle parameters at the time of the fault, including engine speed, load, vehicle speed, and temperatures. This data can help pinpoint specific operating conditions triggering the fault.
Furthermore, the owner mentioned installing a “light assistant-20 group” prior to experiencing the issue. This modification could be a potential source of the problem. It’s possible the new component is:
- Incorrectly Coded: If the new light assistant isn’t correctly coded to the vehicle’s network, it might be sending conflicting signals.
- Wiring Issue: Faulty wiring or a poor connection related to the installation could disrupt communication on the databus.
- Incompatible Hardware: While less likely, the new component might be incompatible with the Caddy’s existing systems.
Other potential causes of a databus implausible message include:
- Faulty Control Module: A malfunctioning control module, not necessarily the engine ECU itself, could be sending incorrect data.
- Wiring Harness Problems: Damage or corrosion in the vehicle’s wiring harness can disrupt communication.
- Low Battery Voltage: Insufficient voltage can cause erratic behavior in electronic systems.
Resolving the Databus Implausible Message
Based on the available information, the following troubleshooting steps are recommended:
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Check Coding of Light Assistant: Verify that the newly installed “light assistant-20 group” is correctly coded to the vehicle using VCDS. Incorrect coding can lead to communication conflicts.
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Inspect Wiring Related to Light Assistant: Thoroughly examine the wiring associated with the light assistant installation. Look for loose connections, damaged wires, or signs of improper installation.
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Check for Other Fault Codes: Although the engine ran fine, review all fault codes in other modules. Sometimes, a seemingly unrelated fault can contribute to communication problems. The fault code present in module 17 (Instruments) and 5F (Information Electronics) indicates potential component protection issues and should be addressed.
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Clear Fault Codes and Retest: After addressing potential issues, clear all fault codes using VCDS and retest the vehicle. This will determine if the problem has been resolved or if further diagnosis is necessary.
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Consult Wiring Diagrams: If the issue persists, consult the vehicle’s wiring diagrams to trace the databus connections and identify potential problem areas.
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Seek Professional Help: If the problem remains unresolved, consult a qualified automotive technician with experience in VW diagnostics. They can perform more advanced troubleshooting and potentially identify a faulty control module or other complex issues.
Conclusion
A “Databus Implausible Message” can be a challenging diagnostic problem. However, by systematically analyzing the fault codes, freeze frame data, and recent modifications, it’s possible to pinpoint the root cause. In this VW Caddy case, focusing on the newly installed light assistant and its integration with the vehicle’s network is the most promising starting point. Remember to always clear fault codes and retest after implementing any changes to confirm the solution’s effectiveness.
