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Siemens Simos8.4 - TC1796

Siemens Simos8.4 - TC1796 FAQ & Error Solutions

Siemens Simos8.4 - TC1796

Errors

Quickly identify common communication and programming issues for the Siemens Simos8.4 control unit.

Files not found

Occurs when the required virtual read file is missing from the bFlash server database.

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71-01-02-03-02 : UDS CheckProgrammingPreconditions RX unexpected size

Triggered by an invalid immobilizer state preventing the programming sequence on VAG vehicles.

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Concerns vehicles from

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Files not found

Method: OBD / Recovery: Bench

Issue: The system cannot locate the corresponding original file on the server during an OBD virtual read operation.

Solution
  • Switch the tool to BENCH mode to perform a physical read of the ECU.
  • Save the read file to your computer.
  • Send the file directly to support@bflash.eu.
  • Wait for our team to add the file to the server for future OBD access.
To understand more

Virtual reading relies on a pre-existing database of original files. When a specific software version is missing, a Bench read is required to capture the full data directly from the TC1796 processor, allowing the file to be cataloged for the community.

71-01-02-03-02 : UDS CheckProgrammingPreconditions RX unexpected size

Method: OBD

Issue: The ECU rejects the programming request because the UDS preconditions (security checks) have failed.

Solution
  • Verify the status of the vehicle's Immobilizer (Immo) system using a diagnostic tool.
  • Ensure the key is recognized and no "Unauthorized" errors are present in the Dashboard or ECU.
  • If the immobilizer is invalid, it must be repaired or synchronized before bFlash (or even OEM tools) can flash the unit.
  • If the issue persists despite a valid immo, Contact our technical support.
To understand more

Modern VAG vehicles using the UDS protocol enforce strict security preconditions. If the Immobilizer is not in a "ready" or "authorized" state, the ECU will return an unexpected response size during the ProgrammingPreconditions check to prevent unauthorized data tampering.