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Diagnostic Trouble Codes

Introduction Diagnostic Trouble Codes, abbreviated DTCs, are the foundation of automotive diagnostics. In essence, they are 3-byte IDs that represent a specific point of failure or problem in your system (to be fair, SAE-J2012 describes them as 2 bytes, whereas ISO-14229 has them as 3 bytes). If there are failures or issues somewhere in your…

UDS Data By Identifier (DID)

Part of a series on UDS – if you missed it, check out the introduction to the protocol. What is it? Data by Identifier, or DID for short, is a core component of building out ECU diagnostics and being able to troubleshoot a malfunctioning ECU. A DID is essentially a piece of data that is…

UDS Security Access

Part of a series on UDS – if you missed it, check out the introduction to the protocol. What is it? Many UDS services, which when executed, could create an unsafe state in the vehicle or reveal sensitive information about the ECU or vehicle. We automotive engineers thus want to ensure that only qualified, authorized…

Diagnostic Sessions and Tester Present

Part of a series on UDS – if you missed it, check out the introduction to the protocol. What’s a Session and Why do I Care? UDS Service 0x10 – Diagnostic Session Control, is one of the most widely used diagnostic services and core to our understanding of the UDS protocol. Session control is a…

UDS Protocol

Protocol Description UDS is a simple client-server centered protocol, with the client sending UDS requests and the server replying with UDS responses. The protocol itself is split into different types of requests, called UDS services, which in turn may (or may not) have sub-services. The client initiates a UDS request by sending the server a…

Unified Diagnostic Services Introduction (UDS)

What is UDS? Chances are if you’ve worked in automotive software, or have an interest in cars, you’ve come across the term UDS. At its core, Universal Diagnostic Services, more commonly known as UDS, is a set of special functions that every vehicle controller is expected to implement to allow external entities the ability to…


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