MANIFOLD-EXHAUST 7W8585 - Caterpillar

System Operation Description:Use this procedure in order to troubleshoot the air shutoff system or use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table
Code and Description Conditions which Generate this Code System Response
446-5 Air Shutdown Relay current below normal The Electronic Control Module (ECM) detects low current in the circuit. The ECM can only detect this condition when the output driver is not activated. The code is logged.
446-6 Air Shutoff Relay short The ECM detects excessive current flow in the circuit. The ECM can only detect this condition when the output driver is activated. The secondary ECM has the ability to stop the engine by shutting off the inlet air supply in an emergency situation. The secondary ECM activates the output driver for the emergency shutdown system. The "Air Shutoff Switch (ASOS)" energizes the two air shutoff solenoids. The solenoids trip the air shutoff valves.There are two conditions which cause the engine control to activate the output driver for the air shutoff relay. The first condition occurs when the operator activates the customer's emergency stop. When the customer's emergency stop button is activated, the emergency stop inputs U and T to the primary ECM and the secondary ECM from the customer connector go high. The secondary ECM will recognize this change. The secondary ECM will energize the output drive for the emergency shutdown system for one second through the diode assembly.The second condition occurs for an engine overspeed. If an engine overspeed occurs, the ECM will activate the output driver for the emergency shutdown system through the diode assembly. An overspeed can be simulated by using Caterpillar Electronic Technician (ET). In order to verify that the overspeed function is operable, the operator must access the screen for overriding parameters on Cat ET. When the override for the engine overspeed is set to the ON position, the setpoint for the engine overspeed is at 75% of the original setpoint. When the engine reaches the modified setpoint, the normal strategy for an engine overspeed is initiated.Relay "R3A" and relay "R3" are energized through terminal 3 of the diode assembly. Terminal 3 of the diode assembly will energize relay "R3A" and relay "R3" for one second. The contacts of relay "R3" keep relay "R3A" and relay "R3" energized until power is cycled. The contacts of relay "R3A" keep the coils of relay "R2" and relay "R2A" energized. When relays "R2" and "R2A" are energized, power is removed from the primary ECM and the secondary ECM. The primary ECM and the secondary ECM will power down. The injection signals to the injector solenoids will stop.The contact of relay "R3A" also supplies power to terminal 3 of the connector for a timer. When power