BOLT 7X2574 - 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    
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 control switch, emergency stop switch, remote start switch, data link and other inputs.The ECM also has outputs that are used for communicating the current state of engine operation. One of the outputs sends a signal to indicate that the crank terminate speed has been achieved. Another output sends a signal that indicates that the engine is running. Both of these outputs are low side ECM drivers. The power for the circuits is provided at the electrical component and the ground circuit is provided by the ECM. Refer to Troubleshooting, "Indicator Lamp - Test" for information that is related to troubleshooting these circuits.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 one of the solenoids that are related to the code. The least likely cause is a problem with the ECM.The ECM supplies +Battery voltage to the start control relay 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 g02025907
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 g02029068
Location of the components for the engine starting system (right side engine view) (1) J2/P2 ECM connectors (2) Electric start control (start control relay)
Illustration 3 g01413257
Location of the connector for the air start control (right rear engine view) (3) Harness connector for the air start control (start control relay)
Thoroughly inspect ECM connectors (1) . Also, thoroughly inspect the other components for the starter circuit that is for your application. Refer to Testing and Adjusting, "Electrical Connectors - Inspect" for details.
Illustration 4 g02029132
Terminal locations at the P2 ECM