COUPLING 4S8855 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit for the Gas Shutoff Valve (GSOV). Also use this procedure if 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    
632-5 Engine Fuel Shutoff Valve #1 : Current Below Normal     The Electronic Control Module (ECM) detects a low current in the circuit for the GSOV for 2 seconds.
The output driver must be off for 5 seconds in order for this code to become active.     The code is logged.
The amber warning lamp is illuminated.
The service tool displays "Error Indicator" on the status screen for this parameter.    
632-6 Engine Fuel Shutoff Valve #1 : Current Above Normal     While the output driver is on for 5 seconds, the ECM detected a high current in the circuit for the GSOV for one second.     The code is logged.
The amber warning lamp is illuminated.
The service tool displays "Error Indicator" on the status screen for this parameter.
The output driver automatically resets and the output driver continues to try to activate the circuit component.    
632-7 Engine Fuel Shutoff Valve #1 : Not Responding Properly     The Engine Control Switch (ECS) is placed in the STOP position. The ECM has shut off the fuel to the engine, but the engine rpm remains above the crank terminate speed. The engine speed exceeded the crank terminate speed for a period that exceeds the "Engine Speed Drop Time".     The code is logged.
The red stop lamp is illuminated.
The power to the GSOV remains in the de-energized state and the ECM removes ignition power from the engine.    The ECM contains the logic and the outputs for control of starting the engine and stopping the engine. Some of the logic for starting the engine and for stopping the engine is customer programmable. The logic responds to inputs from the following components: ECS, emergency stop switch, remote start switch, data link and other inputs.The ECM outputs a signal in order to control the solenoid for the GSOV. To enable gas flow to the engine, the GSOV must be energized.The most likely cause of a diagnostic code is a poor electrical connection or a problem in a wiring harness. The next likely cause may be a problem with the solenoid. The least likely cause is a problem with the ECM.When the 632-7 Engine Fuel Shutoff Valve #1 : Failure occurs, the ECM assumes that the GSOV did not close. The ECM terminates the ignition. If the GSOV does not respond to the ECM command, unburned gas will remain in the air inlet and exhaust system.Note: Ensure that the unburned gas is purged from the exhaust before restarting the engine. Failure to purge the unburned gas from the engine may result in an explosion in the exhaust piping.The following information describes the systems operation when the GSOV is controlled by the ECM:The ECM