UDS protocol

UDS (Unified Diagnostic Services, ISO 14229) is the modern diagnostic application-layer protocol that replaced KWP2000 / KW1281 / K-Line proprietary variants. It defines a standardised set of service identifiers (SIDs) used by every modern ECU read, write, flash and adaptation routine. Runs over CAN (ISO 15765-4), CAN-FD, or DoIP (ISO 13400).

• Standardised service IDs (SIDs) — same request format across Bosch / Siemens / Delphi.
• Session control (DiagnosticSession 0x10) gates which services are available.
• Security access (0x27) is a seed/key challenge gating write/flash operations.
• Routine control (0x31) starts ECU-side routines like checksum or memory erase.
• Request/Transfer/Exit (0x34/0x36/0x37) move flash data into ECU memory.

ID / Code	Name	Purpose
0x10	DiagnosticSessionControl	Enter Default, Extended, Programming, Safety session
0x11	ECUReset	Hard, key-off-on, soft, enable-rapid-power-shutdown
0x14	ClearDiagnosticInformation	Clear stored DTCs
0x19	ReadDTCInformation	Report DTCs by status mask
0x22	ReadDataByIdentifier	Read live or stored data by DID
0x23	ReadMemoryByAddress	Direct memory read (often locked)
0x27	SecurityAccess	Seed/key challenge — gates write/flash
0x28	CommunicationControl	Suppress / resume bus messages
0x2E	WriteDataByIdentifier	Write a calibration ID
0x2F	InputOutputControlByIdentifier	Actuator test
0x31	RoutineControl	Start / stop / status routine (checksum, erase)
0x34	RequestDownload	Begin a memory download into ECU
0x36	TransferData	Send a chunk of memory data
0x37	RequestTransferExit	End a memory transfer
0x38	RequestFileTransfer	File-level transfer (newer ECUs)
0x3D	WriteMemoryByAddress	Direct memory write (often locked)
0x3E	TesterPresent	Keep diagnostic session alive
0x85	ControlDTCSetting	Suppress / enable DTC storage