Figure 6-12 illustrates the EMS used on Caterpillar 3116, 3176, 3406E, and 3500 engines. It is a relatively simple system, without the bells and whistles mandated by current emissions regulations. The ECM mounts on the engine, which reduces the electromagnetic radiation given off by the harness, simplifies packaging, and enables the computer to be cooled by fuel. A major engineering effort was required to isolate the electronics from the heat, vibration, solvents, steam, and water blasts that engines are exposed to.
All sensors, with the exception of the oil pressure sensor, input data for efficient fuel allocation. Abnormally low or high sensor readings cause the ECM to set one or more trouble codes, which can be retrieved by connecting a scan tool to the SAE J1922 data link connector. The only computer-controlled actuators in this particular system are the electronic unit injectors (EUIs), cooling fan, and cruise control.