In vehicle diagnostics using the UDS protocol, when requesting fault codes through service 0x19 (for example, a request like 03 19 02 AF, which means “read DTCs by status mask”), the ECU may respond with multiple frames (multiframe) using ISO-TP due to the amount of data. In this case, the vehicle’s response may begin with a First Frame such as 10 13 59 02 FF 22 74 00, where 10 13 indicates the start and total message length, followed by consecutive frames like 21 64 03 43 00 64 03 68 and 22 00 64 14 4B 00 68 00. To correctly interpret this response, it is necessary to reconstruct all bytes and analyze them in order: 59 02 confirms a positive response, FF represents the status availability mask, and then the DTCs appear, each composed of 3 bytes plus 1 status byte, for example 22 74 00 64 (DTC U2274 with status 0x64), 03 43 00 64 (DTC P0343 with status 0x64), and 14 4B 00 68 (DTC B144B with status 0x68), where the first byte defines the DTC category (P, C, B, or U) and, together with the following bytes, forms the specific fault code. To interpret all this data, I used the CAN Bus Multiplex Trainer tool, which allows me to visualize these frames in real time and analyze each frame individually, facilitating the understanding of how the information is fragmented and reconstructed, which is key to correctly interpreting fault codes and validating diagnostic or emulation processes within the CAN network.
