# TelAF diagnostic

Source: [https://docs.qualcomm.com/doc/80-41102-1/topic/telaf_diagnostic.html](https://docs.qualcomm.com/doc/80-41102-1/topic/telaf_diagnostic.html)

TelAF diagnostic services refer to a set of standardized functions and protocols that
            allow communication between electronic control units (ECUs) within a vehicle and
            external diagnostic tools. These services enable technicians and engineers to monitor,
            diagnose, configure, and troubleshoot the vehicle's electronic systems, components, and
            sensors.

The diagnostic service uses the information exchange initiated by a client to require
            diagnostic information from a server or/and to modify its behavior for diagnostic
            purpose.

The following are some of the primary types of services provided by diagnostic
            services.

- **Diagnostic Session Control**: Diagnostic sessions define the context and scope
                of diagnostic communication. Services related to diagnostic session control allow
                the diagnostic tool to initiate, terminate, and switch between different diagnostic
                sessions based on the tasks being performed.
- **Read Diagnostic Trouble Codes (DTCs)**: This service allows diagnostic tools to
                retrieve stored diagnostic trouble codes (DTCs) from ECUs. DTCs provide information
                about faults or malfunctions in different vehicle systems.
- **Clear Diagnostic Trouble Codes**: Technicians can use this service to clear or
                reset stored DTCs in ECUs after repairs have been performed and issues
                resolved.
- **Communication Control**: These services manage the communication parameters and
                protocols between the diagnostic tool and the ECUs. They ensure that data exchange
                occurs smoothly and efficiently.
- **Security Access Control**: Some diagnostic services require security access to
                perform certain actions, such as ECU programming or advanced configuration. These
                services handle security mechanisms and authorization levels.
- **Upload/Download Data**: Diagnostic services support the transfer of data
                between the diagnostic tool and the ECUs. This can include uploading data from ECUs
                (e.g., event logs) or downloading data to ECUs (e.g., calibration files).

- **[Architecture overview](https://docs.qualcomm.com/doc/80-41102-1/topic/architecture_overview.html)**
- **[Configurations](https://docs.qualcomm.com/doc/80-41102-1/topic/configurations-diag.html)**
- **[Set up diagnostic testing environment](https://docs.qualcomm.com/doc/80-41102-1/topic/set_up_diagnostic_testing_environment.html)**

Last Published: May 12, 2026

[Previous Topic
Limitations](https://docs.qualcomm.com/bundle/publicresource/80-41102-1/topics/limitations.md) [Next Topic
Architecture overview](https://docs.qualcomm.com/bundle/publicresource/80-41102-1/topics/architecture_overview.md)