Unified Diagnostic Services
Unified Diagnostic Services: UDS is the ISO 14229 diagnostic-service family and may be transported over CAN/ISO-TP, DoIP or other supported networks. The page also includes a worked example and measurement sequence.
Technical frame
Unified Diagnostic Services: UDS is the ISO 14229 diagnostic-service family and may be transported over CAN/ISO-TP, DoIP or other supported networks. The page also includes a worked example and measurement sequence.
The technical values here expose the standard, protocol or physical relationship directly; model-specific service values are linked through the matching model/variant dossier.
The goal is not only to define the term but to let the reader calculate and interpret what the data means in a scan, scope or physical test.
Concrete technical facts
- UDS is the ISO 14229 diagnostic-service family and may be transported over CAN/ISO-TP, DoIP or other supported networks.
- 0x10 DiagnosticSessionControl, 0x22 ReadDataByIdentifier, 0x27 SecurityAccess, 0x2E WriteDataByIdentifier and 0x31 RoutineControl are common service identifiers.
- For many services the positive-response SID is request SID + 0x40; a 0x22 request therefore receives 0x62 on success.
- A negative response uses 0x7F + request SID + NRC.
- A valid service can still be rejected when diagnostic session, security level or timing preconditions are not met.
- UDS application behavior must be separated from CAN/DoIP transport faults.
Worked example
- Example: a tester sends 22 F1 90 to read a DID; success starts 62 F1 90 … . If 7F 22 31 is returned, NRC 0x31 indicates request-out-of-range logic rather than a physical bus fault.
Data-structure example
22 F1 90 -> 62 F1 90 ...
7F 22 31 -> negative response, NRC 0x31Measurement and verification sequence
- Capture exact request/response bytes.
- Record diagnostic session and security state.
- Measure P2/P2* timing and transport segmentation behavior.
- Do not confuse an NRC with a physical-network fault.
Fault-separation logic
- Is a valid command present and are power/ground/network healthy?
- Does feedback follow the command?
- Does an independent physical measurement confirm the output?
- Is the fault limited to a specific temperature/load/speed condition?
- Does the result remain stable when the original condition is repeated after repair?
Technical sources
Continue investigating
Model-specific real technical data · Measurement references · Technical diagnostic atlas