A distributed hardware-in-the-loop simulation (HILS) platform is developed for designing an automotive engine control system. The HILS equipment consists of a widely used PC and commercial-off-the-shelf (COTS) I/O boards instead of a powerful computing system and custom-made I/O boards. The distributed structure of the HILS system supplements the lack of computing power. These features make the HILS equipment more cost-effective and flexible. The HILS uses an automatic code generation extension, REAL-TIME WORKSHOP$^{ (RTW$^{) of MATLAB$^{ tool-chain and RT-LAB$^{, which enables distributed simulation as well as the detection and generation of digital event between simulation time steps. The mean value engine model, which is used in control design phase, is imported into this HILS. The engine model is supplemented with some I/O subsystems and I/O boards to interface actual input and output signals in real-time. The I/O subsystems are designed to imitate real sensor signals with high fidelity as well as to convert the raw data of the I/O boards to the appropriate forms for proper interfaces. A lot of attention is paid to the generation of a precise crank/ earn signal which has the problem of quantization in a conventional fixed time step simulation. The detection of injection! command signal which occurs between simulation time steps are also successfully compensated. In order to prove the feasibility of the proposed environment, a simple PI controller for an air-to-fuel ratio (AFR) control is used. The proposed HILS environment and I/O systems are shown to be an efficient tool to develop various control functions and to validate the software and hardware of the engine control system.