UDS

Unified Diagnostic Services (UDS) is the diagnostic protocol defined in ISO 14229. It standardizes the request and response messages a diagnostic tool exchanges with an ECU — for reading identification, reading and clearing fault codes, reading data parameters, performing routines (like an actuator test), and performing ECU reprogramming.

UDS sits above the transport layer (typically ISO-TP / ISO 15765-2 on CAN) and is independent of the wiring. The same UDS service request — say, ReadDataByIdentifier 0xF190 to read a VIN — looks the same on a Class 8 truck and on a passenger car. This standardization is part of why modern diagnostic tools can support a wide range of vehicles without custom code per ECU.

In heavy-duty work, UDS is increasingly common alongside the older J1939 diagnostic services. Newer engine and aftertreatment ECUs often support both: J1939 for the day-to-day fault data, and UDS for deeper diagnostic routines and reprogramming. ecuLink passes both through transparently, so the diagnostic tool decides which protocol to speak on a per-ECU basis.