Common Questions

1. What is the difference between UDS and OBD-II? UDS is a full diagnostic protocol with many services; OBD-II is a subset focused on emissions.

2. Why does my request return NRC 0x7F? 0x7F is a negative response. Check the NRC byte for the specific reason.

3. What is TesterPresent and do I need it? TesterPresent keeps sessions alive. Use it for long operations or extended sessions.

4. How do I know which session a service requires? Consult the service table or switch to extended/programming if you receive 0x7E/0x7F.

5. What is a seed and a key in SecurityAccess? The ECU sends a seed, your tool computes a key using an OEM algorithm.

6. What does RCRRP (0x78) mean and what should I do? It means the ECU accepted the request but needs more time. Wait and retry or listen for the final response.

7. How do I read multiple DIDs in one request? Use uds.read_dids([0xF190, 0xF186]).

8. Can pyudskit connect to a real car? Yes, when paired with a transport (CAN or DoIP). pyudskit focuses on encoding/decoding and workflows.

9. What is the difference between pending and confirmed DTC? Pending is detected once; confirmed is verified across cycles.

10. What are the P2 and P2* timers? P2 is normal response time; P2* is extended time after 0x78.

11. Why do I get conditionsNotCorrect? The ECU state is wrong (session, ignition, vehicle speed, etc.).

12. What is a DID? A Data Identifier used to read or write ECU data.

13. How do I clear DTCs? Use uds.clear_dtcs() which sends 14 FF FF FF.

14. Do I need security access to read data? Not always. Some DIDs require extended session or security access.

15. What is a routine? A predefined ECU function executed via RoutineControl (0x31).

16. What does serviceNotSupportedInActiveSession mean? You are in the wrong session. Switch sessions and retry.