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Siemens Simos18.1 - TC1791

Siemens Simos18.1 - TC1791 FAQ

Siemens Simos18.1 - TC1791

Errors

A quick reference guide to common flashing and communication issues for the Siemens Simos18.1.

71-01-02-03-81

This error indicates that the ECU is currently in a security blocking period preventing any programming operations.

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7F-10-22

Communication is refused because specific safety or vehicle conditions are not currently met.

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7E-00 : UDS CheckProgrammingPreconditions

An unexpected data size was received, usually caused by aftermarket hardware modules interfering with the UDS protocol.

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7F-01-11 : UDS TransferData RX error

The data transfer was interrupted by third-party devices communicating on OBDII Service 01.

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ECU Type unknown/ Error

The specific software version is not in our database and requires a manual reading for identification.

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71-01-02-03-02

Flashing is impossible because the Immobilizer system is currently in an invalid state.

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No data to read

The tool failed to retrieve information, often due to low battery voltage or environment issues.

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could not detect software version

The ECU contains faulty or corrupt programming, making standard OBD communication impossible.

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Concerns vehicles from

Audi Porsche Seat Skoda Volkswagen

71-01-02-03-81

Method: OBD

Issue: The user is unable to start programming because the ECU has activated a security lockout timer.

Solution
  • Switch off the ignition.
  • Close the vehicle completely for a few minutes.
  • Wait for the CAN bus to go into sleep mode.
  • Retry the programming operation.
To understand more

Error 81 translates to "Programming blocking time is active". This is a security feature within the Simos18.1 firmware that triggers after failed attempts or specific sequences, requiring a physical rest period for the module.

7F-10-22

Method: OBD

Issue: The ECU refuses to enter the required programming session due to unmet environmental conditions.

Solution
  • Open the bFlash HELP section for this specific protocol.
  • Ensure all conditions are met (e.g., Engine OFF, Battery > 12.5V, Hood open, Parking brake ON).
  • Clear any existing DTCs before retrying.
To understand more

UDS error 0x22 (Conditions Not Correct) signifies that the Diagnostic Session Control was rejected because the vehicle's state (temperature, voltage, or gear position) does not match the safety requirements for flashing.

7E-00 : UDS CheckProgrammingPreconditions RX unexpected size

Method: OBD

Issue: The programming sequence fails because the UDS response contains data that doesn't match the expected format.

Solution
  • Identify and disconnect non-original modules (Polarfis, monitoring gauges, pedal boxes).
  • Ensure the OBD port is clear of any piggyback devices.
  • Retry the communication with only the bFlash tool connected.
To understand more

This is typically caused by external modules that intercept or modify CAN messages. When bFlash requests programming preconditions, these devices inject data that corrupts the expected UDS packet structure.

7F-01-11 : UDS TransferData RX error.

Method: OBD

Issue: The data transfer is being blocked by concurrent traffic on the vehicle's diagnostic bus.

Solution
  • Remove any third-party diagnostic tools or loggers connected to the vehicle.
  • Ensure no mobile apps are connected via Bluetooth OBD dongles.
  • Retry the write process once the bus is clear.
To understand more

This error indicates that another device is requesting data on Service 01 (OBDII generic). In the UDS protocol, programming requires exclusive access, and interference on Service 01 will abort the TransferData session.

ECU Type unknown/ Error

Method: OBD / Recovery: Boot

Issue: The tool cannot find a matching virtual read or protocol for this specific software version online.

Solution
To understand more

New or rare software versions may not be available for OBD Virtual Read. A physical BOOT connection allows bFlash to extract the full binary directly from the TC1791 processor for analysis.

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

Method: OBD

Issue: Programming is rejected because the ECU detects an immobilizer fault or mismatch.

Solution
  • Verify that the key is recognized and the Immobilizer is active/valid.
  • Check for any 'Immobilizer' related DTCs in the Engine and Dashboard modules.
  • Note: It is impossible to program a VAG vehicle if the immo state is invalid.
To understand more

The Simos18.1 architecture requires a "Handshake" with the Immobilizer before opening programming gates. If the immo is in an error state, the UDS preconditions will fail immediately to protect the car from theft or unauthorized sync.

No data to read : UDS CheckProgrammingPreconditions RX error

Method: OBD

Issue: The tool is unable to establish a stable diagnostic link to begin the reading process.

Solution
  • Open the hood (required for some VAG models to enable OBD writing).
  • Connect a high-quality battery charger (minimum 25A).
  • If the issue persists, Contact our technical support with a screenshot.
To understand more

Lack of data response often points to Voltage instability. Modern ECUs like Simos18.1 consume significant power during diagnostic requests; if the voltage drops slightly, the ECU may terminate the session to prevent data corruption.

could not detect software version

Method: OBD / Recovery: Boot

Issue: The identification process fails because the current software on the ECU is corrupted or incorrectly modified.

Solution
  • Do not attempt further OBD programming.
  • Perform a BOOT recovery to restore the ECU to a functional state.
  • Ensure you have a valid original file or backup before proceeding.
To understand more

If an ECU has faulty content (checksum errors or incomplete flash), the OBD stack might not initialize correctly. A BOOT recovery bypasses the faulty software and communicates directly with the processor to fix the image.