SHAFT AS 7T3120 - Caterpillar

System Operation Description:The Electronic Control Module (ECM) has the ability to stop the engine in an emergency situation by shutting off the intake air supply. The ECM activates two relays which energize the two air shutoff solenoids. The solenoids trip the air shutoff valves. The presence of a switch at each air shutoff valve informs the ECM that the air shutoff solenoids have activated. Unless the air shutoff valves are manually opened, the ECM will not attempt to restart the engine.There are two conditions which cause the engine control to activate the air shutoff relay. The first condition occurs when the operator initiates a remote shutdown. If the customer's emergency stop is activated, the shutdown inputs to the ECM are open. This signals the ECM to turn on the output for the air shutoff relays. The ECM will hold the air shutoff relays active for 1.5 seconds. The second condition occurs for an engine overspeed. The engine overspeed could be an actual overspeed or a simulated overspeed. The simulated overspeed can be obtained by using the overspeed verify switch. When the overspeed verify switch is activated, the ECM will activate the output for the air shutoff relays at 75 percent of the overspeed setpoint.The air shutoff relays can also be activated without the aid of the ECM. When the emergency stop on the instrument panel is depressed, the air shutoff relays are activated. The air shutoff timer will allow the air shutoff relays to deactivate after 2.5 seconds in order to prevent damage to the air shutoff solenoids.Regardless of the reason for activation, the Engine Control Switch (ECS) must be turned to the OFF/RESET position for three seconds in order to reset the ECM and the air shutoff timer. The operator must manually open the air shutoff valves in order to reset the switches at the air shutoff valves.
Illustration 1 g01019840
Typical exampleTest Step 1. Check for Connector Damage.
Turn the circuit breaker for the