Error code occurred during ECU upgrade (5100-04-0002, 5021-27-7F24)

Oscar Eom

22 August 2025 04:55 Updated

Error Code 5100-04-0002 : VCI Mode Change Failure

Check that the target ECU is properly installed in the vehicle. (Depending on the vehicle grade, some ECUs may not be installed.)
Before performing an ECU upgrade, you must run a DTC (Diagnostic Trouble Code) scan once to change the operating mode of the Vehicle Communication Interface (VCI, VCI2, VCI3).
Since the Vehicle Communication Interface can switch from diagnostic mode to ECU upgrade mode, running a DTC scan aligns the VCI in diagnostic mode and prepares it for ECU upgrade.
Test with a spare VCI (VCI, VCI2, VCI3) to determine whether the issue is with the interface itself or the vehicle.
If this error occurs during recovery after a failed SW update, please contact the vehicle quality department or the ECU manufacturer.

This occurs when the ECU sends a 24 Negative Response (Request Sequence Error).
You must check whether the Vehicle Communication Interface (VCI, VCI2, VCI3) in use is functioning properly.
Perform an upgrade test using a spare VCI (VCI, VCI2, VCI3).
Also test the connection between the VCI and the tablet PC using both wired and wireless (Bluetooth, Wi-Fi Direct) methods.
If the upgrade still fails after multiple tests, please contact support with the vehicle’s VIN.
Submitted inquiries are handled in order, so please wait for a service engineer’s response.