TUBE 3161156 - Caterpillar

Electronic Control Module Power Circuit (Electronically Controlled Engines)
The electronically controlled engine uses a wide variety of electronic input devices. These components require an operating voltage. Also, these components could require a reference voltage.The electronic control modules on these engines are not sensitive to the common external sources of noise. However, electro-mechanical buzzers can cause disruptions in the power supply. If electro-mechanical buzzers are used near the engine, the engine electronics should be powered directly from the battery system through a dedicated relay. The engine electronics should not be powered through a common power bus with other devices that are activated by the keyswitch.The ordinary switch input circuits inside the Electronic Control Module (ECM) have a tolerance for resistance and a tolerance to shorts between wires. The tolerances are listed below.
The Electronic Engine Control System will tolerate resistance in any ordinary switch up to 2.5 Ohms without malfunctioning.
In any ordinary switch input, the Electronic Engine Control System will tolerate shorts between wires to 5000 Ohms without a malfunction.
The +24 Volt wire in the data link harness of the ECM is provided to power the Electronic Engine Control System service tools only. No other devices should be powered by this wire. The ECM was not designed to carry high current loads and is not short circuit protected.
The ECM draws a maximum of 6.5 Amperes at 24 volts from the electrical system under steady state conditions. While you are starting the engine, the ECM will draw a maximum of 9 Amperes. However, the Electronic Engine Control System will function with less than 24 volts. A minimum of 8 volts is required when the engine is cranked. A minimum of 24 volts is needed when the engine is running.Power enters the ECM through the + battery wire. Power exits the ECM through the negative battery wire. The Electronic Engine Control System is protected against power surges on the 24 Volt power supply. These power surges are due to alternator load dumps and due to jump starting with voltages up to 32 volts.Engine Speed Input Circuit
Engine speed is sensed by an electronic engine speed sensor. This is similar to an electromagnetic pickup. The signal is generated by placing the sensor near a rotating component. However, the sensor requires an operating voltage. The sensor requires an operating voltage of 8.0 0.4 Volts. This voltage is provided by the ECM.The output of the engine speed sensor is a voltage pulse. The frequency is dependent on the speed of the engine. The frequency of the pulse is interpreted by the ECM as engine speed. When you crank the engine, the frequency of the signal is 10 to 50 Hz (Hertz). The frequency of the signal is approximately 120 Hz at low idle.Fuel Rack Input Circuit
The engine fuel rack signal is obtained from an electronic linear position sensor. The sensor follows the movement of the rack assembly. This sensor requires an operating voltage of 8.0 0.4 Volts. The sensor requires a reference voltage of 5.0