ROD AS 4T6838 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the start/run/stop circuit or if the diagnostic code in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table
Description Conditions which Generate this Code System Response
336-2 Engine Control Switch erratic, intermittent, or incorrect The inputs from the start/run/stop switch are in a different 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 know 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. When both of the 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. If this occurs, you must use the emergency stop switch or you must 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 at the beginning of a crank cycle, 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 g01934723
Typical schematic
Illustration 2 g01259533
P1 ECM connector
(P1-21) Start/Run/Stop switch 3
(P1-22) Start/Run/Stop switch 4
Illustration 3 g01973157
P2 ECM connector
(P2-6) Digital return
Illustration 4 g01234146
Location of ECM connectors
Illustration 5 g01259500
Connector "A"
(Terminal 25) Digital return
Illustration 6 g01259501
Connector "B"
(Terminal 2) Start/Run/Stop switch 3
(Terminal 3) Start/Run/Stop switch 4
Illustration 7 g01259503
Connector "G"
(Terminal 4) Start/Run/Stop switch 4
(Terminal 6) Start/Run/Stop switch 3
(Terminal 37) Digital return Test Step 1. Inspect Electrical Connectors and Wiring
Turn the breaker for the ECM to the OFF position.
Thoroughly inspect the ECM connectors. Inspect all of the other connectors for the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and the wiring for abrasion and for pinch points. Expected Result:All connectors, pins, and sockets are completely