Application of J1939 to J1708 Cable in Automotive Diagnosis

With the rapid development of automotive electronic technology, the diagnostic system of vehicles is also constantly upgrading and improving. In the field of automotive diagnostics, J1939 and J1708, as two important communication protocols, each have unique application scenarios and advantages. However, due to differences in vehicle manufacturing year, brand, and model, many modern vehicles use J1939 protocol for communication, while some older vehicles still use J1708 protocol. In order to meet the needs of cross protocol diagnosis, J1939 to J1708 cables have emerged and play an important role in automotive diagnosis.

1、 Overview of J1939 and J1708 protocols

The J1939 protocol is a communication protocol defined by the Society of Automotive Engineers (SAE) for heavy-duty vehicles and industrial equipment, primarily used for real-time data exchange between vehicles and equipment. It is based on CAN (Controller Area Network) bus technology, using 29 bit extended identifiers and extended data frames. The CAN communication rate is 250Kbps, which can efficiently transmit various diagnostic information, fault codes, and control commands of the vehicle.

In contrast, the J1708 protocol is an SAE standard based on RS-485, mainly used for serial communication in agricultural vehicles, commercial vehicles, and heavy machinery. It defines a 2-wire 18 gauge cable with a communication rate of 9600 bit/s during operation and a length of up to 40 meters. The J1708 protocol is more common in older vehicle systems, used to transmit vehicle status information and control signals.

2、 Application of J1939 to J1708 Cable in Automotive Diagnosis

In the field of automotive diagnostics, J1939 to J1708 cables are mainly used to connect diagnostic equipment based on the J1939 protocol with old vehicles based on the J1708 protocol. This cable conversion technology enables modern diagnostic equipment to read and analyze fault information of old vehicles, greatly improving the efficiency and accuracy of diagnosis.

Fault code reading: Through the J1939 to J1708 cable, diagnostic equipment can read fault codes in old vehicles, which are usually stored in the vehicle's ECU (Electronic Control Unit). The diagnostic equipment will provide corresponding fault descriptions and possible solutions based on the read fault codes, helping maintenance personnel quickly locate and repair the fault.

Real time data monitoring: In addition to reading fault codes, the J1939 to J1708 cable can also be used to monitor real-time data in old vehicles, such as engine speed, vehicle speed, fuel consumption, etc. These data are of great significance for diagnosing vehicle performance issues and optimizing driving behavior.

Control command sending: In some cases, maintenance personnel may need to send control commands to the vehicle through diagnostic equipment to perform specific tests or adjustments. The J1939 to J1708 cable can ensure that these control commands are correctly sent to the ECU of old vehicles, thereby achieving the required testing or adjustment.