| Field | UDS Name | Typical Content |
|---|---|---|
| Record number | snapshotRecordNumber | 0x01 (first occurrence); 0xFF = most recent |
| Odometer | OdometerMaster | Vehicle km at time of DTC confirmation |
| Vehicle speed | VehicleSpeed_F40 | km/h at time of confirmation |
| Engine RPM | EngineSpeed_F30 | RPM at time of confirmation |
| Engine coolant temp | EngineCoolantTemp_F05 | °C at confirmation |
| Battery voltage | BatteryVoltage | mV; useful for detecting brownout faults |
| DTC trigger DID | ApplicationDID_0101 | Any application DID relevant to the fault |
DTC Snapshot (Freeze Frame) Records
AUTOSAR DEM Freeze Frame Configuration
XMLDem_FreezeFrame.arxml
FreezeFrameClass_Standard
0xF40D
2
0xF406
1
0x0101
1
3
OBD-II Freeze Frame vs UDS Snapshot
| Aspect | OBD-II Freeze Frame (0x02 Mode 2) | UDS Snapshot (0x19 0x04) |
|---|---|---|
| Standard | SAE J1979 / ISO 15031-5 | ISO 14229-1 |
| Content | Mandated PIDs: speed, RPM, coolant, MAP, etc. | OEM-defined DIDs; any application data |
| Storage | 1 freeze frame per confirmed MIL-triggering DTC | Multiple snapshots per DTC (OEM configurable) |
| Access | OBD-II Mode 2 (any scanner) | UDS 0x19 0x04 (workshop only) |
| Clear | Cleared by Mode 4 (OBD clear) | Cleared by 0x14 (UDS clear) |
Summary
Freeze frames are the black box recorder for DTCs — they capture the vehicle state at the moment of DTC confirmation, not at first detection. Configure freeze frames to include the application signals most diagnostic for each DTC: a speed sensor fault should capture vehicle speed and wheel speeds; a fuel pressure fault should capture engine RPM and throttle position. The DEM storage limit (NvM block size) forces a trade-off between snapshot DID count and number of stored snapshots per DTC — three snapshots at moderate content is usually more useful than one snapshot with exhaustive content.
🔬 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.