BOLT 7X0392 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the start/stop circuit. Also, use this procedure if the following diagnostic code is active or easily repeated.
Table 1
Diagnostic Code Table
J1939 Code and Description Conditions which Generate this Code System Response
1656-2
Engine Automatic Start Enable Switch : Erratic, Intermittent, or Incorrect The two inputs from the ECS are in the opposite state. The code is logged. The Electronic Control Module (ECM) receives two input signals from the start/run/stop switch. The two input signals should have the same logic level. If two different signals are detected during the powerup, the ECM will determine that one of the signals is incorrect. The duplication of the signals permits the ECM to detect if there is a problem in the wiring.When both of the input signals are high or open, the ECM assumes that the start/run/stop switch is in the STOP position. If both input signals are low or shorted to the digital return terminal, the ECM assumes that the start/run/stop switch is in the START position. After the start/run/stop switch is turned to the START position, the ECM will initiate the starting sequence. The ECM will energize the prelube system if the prelube system is available and activated. After the prelube cycle is completed, the ECM will energize the start enable relay. If both of the signals go high or open while the engine is running, the engine will stop.If the engine is running and one of the inputs from the start/run/stop switch changes states, the ECM will ignore the inputs from the start/run/stop switch until power is cycled to the ECM. Use the emergency stop switch or disconnect the power to the ECM in order to shut down the engine.If the inputs from the start/run/stop switch are in opposite states, the ECM will not initiate the crank cycle. A diagnostic code will be logged and a diagnostic code will be active for this problem. The diagnostic code for this problem will be active until the ECM is powered down.
Illustration 1 g03392065
Illustration 2 g03325748
P1 ECM connector
(P1-40) Run/Stop 1
(P1-54) Run/Stop 2
Illustration 3 g03393083
P2 ECM connector
(92) Digital return
Table 2
1. Inspect the Electrical Connectors and Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect the connectors for the stop switches and the J1/P1 ECM connector.
a. Check for a loose connection or check for poor connections at the connector for the stop switches.
b. Check connections between the stop switches and the ECM.
Refer to Troubleshooting, "Electrical Connectors - Inspect" for information related to inspecting the electrical connectors and wiring.
C. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the stop switches.
D. Check the allen head screw for each of the ECM connectors for the proper torque.
Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
E. Check the harness and wiring for abrasion and for pinch points from the stop switches to the ECM.
Connectors and Wiring
Result: The harness and the wiring appear