UDS services
Negative response codes
From ISO 14229-1. Codes 0x38–0x4F are reserved for extended data-link security and 0x50–0x5D are used by the Authentication service in the 2020 edition. Manufacturer-specific codes are not listed.
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Questions
What does 7F mean in a UDS response?
0x7F marks a negative response. The next byte is the service that was requested and the last byte is the negative response code (NRC) that explains why it was refused.
What does NRC 0x78 mean?
Response pending: the request was received correctly but the ECU needs more time. It is not an error; the tester should wait for the final response.
How are DTCs stored in bytes?
The first two bits give the area (P, C, B or U), the next two the first digit and the remaining 12 bits the last three hex digits. UDS adds a third byte, the failure type byte, that describes the kind of fault, such as 0x13 circuit open.
Building or testing diagnostics?
Dervo engineers test UDS diagnostics, flashing and DTC handling with automated scripts on HIL benches and in vehicles.