UDS 27服务NRC

### UDS ISO 14229-1 Diagnostic Service 27 NRC Meaning and Solutions Service $27$ in the Unified Diagnostic Services (UDS) protocol, as defined by ISO 14229-1, is used for Security Access. This service allows a diagnostic tool to gain access to certain security levels within an Electronic Control Unit (ECU). The Negative Response Codes (NRCs) associated with this service provide information about why a request was not successfully processed. #### Common NRCs Related to Service $27$ Some of the common NRCs encountered when using Service $27$ include: - **0x12**: Sub-function Not Supported or Incorrect Format[^1]. This indicates that either the sub-function requested does not exist on the ECU or there has been a formatting error. - **0x13**: Request Out Of Range[^1]. Occurs when parameters provided are outside acceptable limits set by the manufacturer. - **0x22**: Conditions Not Correct/Request Sequence Error[^1]. Indicates improper sequencing during communication; typically seen if commands do not follow expected order. - **0x2E**: Security Access Denied[^1]. Returned when authentication fails due to incorrect key submission or other issues preventing successful verification. - **0x78**: Request Correctly Received – Short Time Delay Required Before Resending[^1]. Suggests temporary unavailability because processing might still be ongoing from previous requests. For resolving these errors effectively, it's important first to verify all data being sent matches specifications outlined by vehicle manufacturers exactly. For instance, ensuring proper seed-and-key exchanges occur without timing discrepancies can prevent many typical failures related specifically to security access procedures. When encountering `Security Access Denied` responses (`0x2E`), double-checking both hardware connections along with software configurations becomes crucial since miscommunication between devices could lead directly back into failed authentications repeatedly until corrected properly. ```python def check_nrc(nrc_code): nrc_meanings = { '0x12': "Sub-function Not Supported or Incorrect Format", '0x13': "Request Out Of Range", '0x22': "Conditions Not Correct/Request Sequence Error", '0x2E': "Security Access Denied", '0x78': "Request Correctly Received – Short Time Delay Required Before Resending" } return nrc_meanings.get(nrc_code, "Unknown NRC Code") print(check_nrc('0x2E')) ```