RING 7J1938 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the air shutoff system or if any one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table
Description Conditions which Generate this Code System Response
446-5 Air Shutoff Relay open The Electronic Control Module (ECM) detects an open circuit and/or a short to the +Battery in the solenoid circuit. The ECM can only detect this condition when the sourcing driver for the air shutoff solenoid is not energized. The code is logged.
446-6 Air Shutoff Relay short The ECM detects a short circuit to ground in the solenoid circuit. The ECM can only detect this condition when the sourcing driver for the air shutoff solenoid is energized. The air shutoff relays can 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 2.4 seconds in order to prevent damage to the air shutoff solenoids.The 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. There are three conditions which can cause the ECM to activate the air shutoff:Engine Overspeed - The first condition occurs when the ECM detects an engine overspeed. During an engine overspeed, the ECM energizes the air shutoff relays. The ECM supplies voltage to the air shutoff relays for 2.4 seconds. The output of the relay will energize the air shutoff solenoids in order to shut down the engine.Emergency Stop Sequence - The second condition occurs when the operator initiates a remote shutdown. If the customer's emergency stop is activated, the shutdown inputs to the ECM are opened. This signals the ECM to turn on the output for the air shutoff relays. The ECM will hold the air shutoff relays active for 2.4 seconds.Overspeed Verify Feature - The third condition occurs when the overspeed verify feature is initiated with Caterpillar Electronic Technician (ET). This feature will energize the air shutoff relays when the engine speed is increased above 75 percent of the rated engine speed. The ECM supplies voltage to the air shutoff relays for 2.4 seconds during the shutdown. The overspeed verify feature can be initiated in order to test the operation of the air shutoff system.Regardless of the reason for activation, the Engine Control Switch (ECS) must be turned to the OFF 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 g01949553
Typical schematic
Illustration 2 g01216447
P1 ECM connector
(P1-5) Digital return
(P1-23) Engine shutdown "C"
(P1-28) Engine shutdown