Open a UDS (ISO 14229) diagnostic session over CAN and read stored DTCs from an ECU.
domain: iso.org · 6 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Establish the transport layer, typically ISO-TP over CAN (ISO 15765-2), addressing the target ECU's request/response CAN IDs.
Send a DiagnosticSessionControl request (service 0x10) to move from the default session into an extended or programming session as needed.
Complete SecurityAccess (service 0x27) seed/key exchange if the target data or sub-function requires it.
Send ReadDTCInformation (service 0x19) with the appropriate sub-function, such as reportDTCByStatusMask, to retrieve stored DTCs and status bytes.
Send periodic TesterPresent (service 0x3E) requests to keep a non-default session alive during a longer diagnostic sequence.
Optionally clear codes with ClearDiagnosticInformation (service 0x14) once the DTCs have been logged.
Known gotchas
The full ISO 14229 text is a paid standard; exact sub-function byte layouts in practice are commonly cross-checked against OEM-specific diagnostic databases, not just the base spec.
Sessions time out (commonly around 5 seconds) without TesterPresent, silently dropping the ECU back to the default session mid-sequence.
Security-gated ReadDTCInformation sub-functions return a negative response code if SecurityAccess wasn't completed first — don't interpret an NRC as 'not supported' without checking the code.
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