SHOE-CIRCLE GUIDE 3120780 - Caterpillar

System Operation Description:Use this procedure to troubleshoot a suspected problem with the engine starting system. Also, use this procedure if one of the diagnostic codes in Table 1 are active or easily repeated.
Table 1
Diagnostic Codes Table    
J1939 Code and Description    Conditions which Generate this Code    System Response    
677-5 Engine Starter Motor Relay : Current Below Normal     The Electronic Control Module (ECM) detects an open in the circuit for the start control relay for more than 5 seconds.
The output driver must be off in order for this code to become active.     The code is logged.
The amber warning lamp is illuminated.    
677-6 Engine Starter Motor Relay : Current Above Normal     The ECM detects a short in the circuit for the start control relay for more than 5 seconds.
The output driver must be on in order for this code to become active.     The code is logged.
The amber warning lamp is illuminated.    The engine ECM contains the logic and the outputs for starting the engine. The logic for starting the engine is customer programmable. The logic responds to inputs from the following components: engine start control, emergency stop switch, remote start switch, data link and other inputs.The most likely causes of any of these diagnostic codes are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with the starter solenoid. The least likely cause is a problem with the ECM.The ECM supplies +Battery voltage to the starter solenoid when the logic determines the necessity. The ECM removes the voltage when the crank terminate speed has been achieved. Also, if the timer for the "Cycle Crank Time" parameter is exceeded, voltage will be removed from the start control relay.
Illustration 1 g02692876
Schematic for the components of the engine starting systemTest Step 1. Inspect the Electrical Connectors and the Wiring
Remove the electrical power from the ECM.
Illustration 2 g02692918
Location of the components for the engine starting system (right side engine view) (1) J1/P1 ECM connectors (2) J2/P2 ECM connectors (3) Engine harness connector (for incendive components)
Illustration 3 g02692996
Location of the connector at the starter motor (right rear engine view) (4) Harness connector for the starter solenoid
Illustration 4 g02692956
Location of the connector for the starter relay (right rear engine view) (5) Relay connector for the air start relay
Thoroughly inspect ECM connectors (1) and (2) . Also, thoroughly inspect the connectors for the starter circuit that is for your application. Refer