SEAL-THREAD 8J6775 - Caterpillar

System Operation Description:The master 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.Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.The most likely causes of the diagnostic code are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with a starter motor magnetic switch. The least likely cause is a problem with the master ECM.The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.Electric StartThe master ECM supplies +battery voltage to two magnetic switches when the logic determines that it is necessary. Each magnetic switch provides +battery voltage to a solenoid on an electric starting motor.The master ECM removes the voltage when the crank terminate relay is energized. The voltage is also removed if the customer programmable "Overcrank Time" has expired.Air StartThe master ECM supplies +battery voltage to the air start relay when the logic determines that it is necessary. The master ECM removes the voltage when the crank terminate relay is energized. The voltage is also removed if the customer programmable "Overcrank Time" has expired.If the engine is equipped with a prelubrication system, an air start may not occur until the prelubrication is complete. If there is a problem with the prelubrication system, the air start may not occur. There are no diagnostics for the prelubrication system. Refer to Systems Operation, Testing and Adjusting, "Air Starting System (Starting with an Air Prelube Pump)".
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Schematic for the electric starting system
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Schematic for the air starting systemTest Step 1. Inspect the Electrical Connectors and Wiring
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Terminal box for the master ECM (1) J2/P2 connectors for the master ECM (2) J14/P14 connectors for the harness from the starting system (3) 16 amp circuit breaker
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(4) Junction box for the starter motor magnetic switches
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Junction box for the starter motor magnetic switches (5) Magnetic switches (6) Connections for the magnetic switches
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Typical air start relay and connector (7) Air start relay (8) Connector for the air start relay
Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
Thoroughly inspect the following connectors and the wiring harnesses for the connectors:
Master ECM J2/P2 connectors
J14/P14 connectors
Connectors for the air start relay (if equipped)
Connections for the starter motor magnetic switches (if equipped)
Check the torque of the Allen head screw for the ECM connectors. The proper torque is 6 1 N m (55 9 lb in).
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Harness side of the master ECM P2 connector (P2-10) Start command (P2-20) Return for the start command
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(9) P14 connector for the harness from the