Reprogramming Sequence Overview - UDS Diagnostics

Complete UDS Reprogramming Sequence

Step-by-Step Flash Reprogramming (ISO 14229 / OEM Extension)

  1. Extended Diagnostic Session (0x10 0x03)
  2. Communication Control: disable non-diagnostic CAN TX (0x28 0x03 0x01)
  3. SecurityAccess Level 1 (0x27 0x01/0x02)  [if required before session jump]
  4. Programming Session (0x10 0x02)
  5. SecurityAccess Level 2 (0x27 0x03/0x04)  [reprogramming access]

  ── For each flash block (SBL, App, Cal): ─────────────────────────
  6. RoutineControl: Erase Memory (0x31 0x01 0xFF 0x00 + start/size)
     → NRC 0x78 × N while erasing; positive response when complete
  7. RequestDownload (0x34): declare block start address + length + compression
  8. TransferData (0x36) × N: send blocks of data (blockSequenceCounter 0x01..N)
  9. RequestTransferExit (0x37): end transfer; ECU verifies internal CRC
  10. RoutineControl: Check Programming Dependencies (0x31 0x01 0xFF 0x01)
  ── End of per-block loop ─────────────────────────────────────────

  11. RoutineControl: Check Memory (0x31 0x01 0x02 0x02) [optional: final integrity]
  12. ECUReset Hard Reset (0x11 0x03) → ECU boots from new firmware
  13. Re-enter Extended Session; verify SW version DID 0xF189 updated

Pre-conditions for Reprogramming

Condition	Rationale	Check Method
Vehicle stationary (speed = 0)	Flash programming disables ECU function; not safe while driving	Read DID 0xF40D (speed) before session jump
Battery voltage 11.5V–14.5V	Voltage drop during erase causes incomplete erase → bricked ECU	Read DID 0xFD01 (battery voltage)
Engine off (ignition-on only)	High current draw during flash interferes with ECU operation	Check ignition state via DID
TesterPresent during programming	S3 timeout during flash = session reset mid-write = bricked ECU	Send 0x3E 0x80 every 2s throughout; automate in tester
Sufficient NvM space	DEM/NvM operations paused during programming	Implicitly checked by bootloader at Programming Session entry

Flash Block Layout

Block	Content	Addresses (Aurix TC397 example)	Reprogrammable?
Boot Manager	First-stage bootloader; never erased	0x80000000–0x8001FFFF	No (hardware protected)
SBL (Secondary Bootloader)	UDS programming handler; downloaded first	0x80020000–0x8007FFFF	Yes (after Boot Manager validates)
Application	Main ECU software	0x80080000–0x807FFFFF	Yes (after SBL validates)
Calibration	OEM calibration data	0x80800000–0x80FFFFFF	Yes (separately from application)

Summary

The reprogramming sequence has two distinct phases: application-side UDS communication (steps 1–5) handled by the running application; and bootloader-side flash operations (steps 6–12) handled by the SBL after the application transfers control. The battery voltage and vehicle speed pre-conditions are not optional — an incomplete erase cycle caused by a voltage brownout creates a partially-erased flash block that the bootloader cannot execute, requiring a bench recovery with JTAG. Pre-condition checks before entering Programming Session prevent the majority of field bricking incidents.

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.

🏭 How This Topic Appears in Production Projects

Project integration phase: The concepts covered in this lesson are most commonly encountered during ECU integration testing — when multiple software components from different teams are combined for the first time. Issues that were invisible in unit tests frequently surface at this stage.
Supplier/OEM interface: This is a topic that frequently appears in technical discussions between Tier-1 ECU suppliers and OEM system integrators. Engineers who can speak fluently about these details earn credibility and are often brought into critical design review meetings.
Automotive tool ecosystem: Vector CANoe/CANalyzer, dSPACE tools, and ETAS INCA are the standard tools used to validate and measure the correct behaviour of the systems described in this lesson. Familiarity with these tools alongside the conceptual knowledge dramatically accelerates debugging in real projects.

⚠️ Common Mistakes and How to Avoid Them

Assuming default configuration is correct: Automotive software tools ship with default configurations that are designed to compile and link, not to meet project-specific requirements. Every configuration parameter needs to be consciously set. 'It compiled' is not the same as 'it is correctly configured'.
Skipping documentation of configuration rationale: In a 3-year ECU project with team turnover, undocumented configuration choices become tribal knowledge that disappears when engineers leave. Document why a parameter is set to a specific value, not just what it is set to.
Testing only the happy path: Automotive ECUs must behave correctly under fault conditions, voltage variations, and communication errors. Always test the error handling paths as rigorously as the nominal operation. Many production escapes originate in untested error branches.
Version mismatches between teams: In a multi-team project, the BSW team, SWC team, and system integration team may use different versions of the same ARXML file. Version management of all ARXML files in a shared repository is mandatory, not optional.

📊 Industry Note

Engineers who master both the theoretical concepts and the practical toolchain skills covered in this course are among the most sought-after professionals in the automotive software industry. The combination of AUTOSAR standards knowledge, safety engineering understanding, and hands-on configuration experience commands premium salaries at OEMs and Tier-1 suppliers globally.