A scan using VCDS (Vag-Com Diagnostic System) on a 2012 Golf revealed several fault codes, even though the MIL (Malfunction Indicator Lamp) wasn’t illuminated. Attempts to clear these codes through VCDS resulted in an error message: “The request to clear codes was not acknowledged by the engine control module. DTCs in this controller might only be cleared through an OBD2 broadcast. This will erase fault codes in all OBD2 systems. Do you want to proceed?”
Understanding the VCDS Error Message
This error message indicates that the engine control module (ECM) is preventing VCDS from directly clearing the fault codes. It suggests using an OBD2 broadcast command, which clears codes across all systems in the vehicle that comply with OBD2 standards. While this approach can be effective, it’s important to understand why the ECM might be blocking the initial clearing attempt.
Troubleshooting Steps
After encountering the “request to clear codes was not acknowledged” message and the subsequent unsuccessful “Restarting session,” further diagnostic steps were taken:
- Manual OBD2 Mode 03 and Mode 07 Checks: Accessing the OBD2 system directly through VCDS and selecting Mode 03 (Emission related fault codes) and Mode 07 (Pending emission related fault codes) for address 7E8 yielded no fault codes. This result seems contradictory to the initial VCDS scan that showed faults in multiple modules.
Potential Causes and Solutions
The discrepancy between the initial fault code scan and the inability to clear codes, along with the negative results from Mode 03 and Mode 07, suggests several possibilities:
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Communication Issues: A problem with the communication between VCDS and the vehicle’s various control modules could be causing the issue. This could be due to a faulty OBD2 cable, a problem with the vehicle’s CAN bus system, or even a software glitch within VCDS itself. Checking connections, updating VCDS software, and testing with a different OBD2 cable could help diagnose this.
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ECM Malfunction: A malfunctioning ECM could prevent communication and the clearing of codes. Further diagnostics on the ECM itself might be required.
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Immobilizer Issues: The presence of fault code P1570 (Engine Start Blocked by Immobilizer) in the engine module suggests a potential problem with the immobilizer system. This could be related to the key, the immobilizer control module, or the wiring between them. Resolving this issue might allow the other codes to be cleared.
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Low Voltage: While the VCDS log shows a reasonable battery voltage, a temporary voltage drop during the clearing process could disrupt communication and prevent the codes from being erased. Ensuring a stable voltage supply during the procedure is crucial.
Using VCDS to Clear MIL: Best Practices
When using VCDS to clear your MIL, keep the following in mind:
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Ensure Proper Connection: Double-check your OBD2 cable connection and ensure your laptop is properly communicating with the VCDS interface.
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Update VCDS Software: Using the latest version of VCDS ensures compatibility with the vehicle’s systems and access to the latest features and bug fixes.
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Address Underlying Issues: Simply clearing codes without addressing the underlying problems will likely result in the MIL returning. Thoroughly diagnose and repair any faults before clearing codes.
Conclusion
Clearing fault codes with VCDS can sometimes be more complex than simply selecting the “Clear Codes” function. When encountering the error message preventing code clearing, a systematic approach to troubleshooting is necessary. Investigating communication issues, addressing immobilizer problems, and ensuring a stable voltage supply are crucial steps in successfully using VCDS to clear your MIL. Always remember to diagnose and repair the underlying issues causing the fault codes to prevent their recurrence.
