Engine Control Switch - Test
Use this procedure to troubleshoot the electrical system if a problem is suspected with the start/stop circuit.
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. 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.
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| Illustration 1 | g03323564 |
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| 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 to be OK. Proceed to Test Step 2. Result There is a problem in the harness connectors and/or the harness. Repair: Repair the harness connectors or the harness. Ensure that all of the seals for the connectors are properly in place and ensure that the connectors are coupled. Verify that the repair eliminates the problem. STOP |
| 2. Check the Status of the Switch using Caterpillar Electronic Technician (ET) A. Connect Caterpillar Electronic Technician (ET) to the service tool connector. B. Restore the electrical power to the ECM. C. Monitor the status of the start/run/stop switch using Cat ET. D. Turn the start/run/stop switch to the STOP position. E. Turn the start/run/stop switch to the START position. F. Turn the start/run/stop switch to the STOP position. |
ECS Status and Active 1656-2 Diagnostic Code |
Result: The status for the switch is correct in both the START and STOP positions. A diagnostic code for the switch is not active. Repair: The switch appears to be operating correctly. There may be an intermittent problem in the harness or in a connector. For information related to identifying intermittent electrical problems, refer to Troubleshooting, "Electrical Connectors - Inspect". STOP Result: The parameter for the switch is not correct in either the STOP or the START positions. Proceed to Test Step 3. |
| 3. Check the Wiring for an Open Circuit A. Turn the main disconnect switch to the OFF position. B. Disconnect the J1/P1 and the J2/P2 ECM connector . C. Remove the wires from the switch. D. Install a wire jumper between the wires 11 and 6 at the switch. E. Measure the resistance between P1-21 and P1-22 at the P1 ECM connector. F. Return all wiring to the original configuration. |
Continuity Between P1-21 and P1-22 |
Result: The measurement indicated a short circuit. The circuit is OK. Proceed to Test Step 4. Result: The measurement indicated an open circuit. Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the repair eliminates the problem. STOP |
| 4. Check the Harness Wiring for a Short Circuit A. Disconnect the J1/P1 and J2/P2 ECM connector. B. Measure continuity between terminal P1-21 and every terminal on the P1 ECM connector and the P2 ECM connector. C. Measure continuity between P1-21 and engine ground. D. Measure continuity between terminal P1-22 and every terminal on the P1 ECM connector and the P2 ECM connector. E. Measure continuity between P1-22 and engine ground. F. Return all wiring to the original configuration. |
No Continuity |
Result: There is no continuity between P1-40/P1-54 and the other circuits at the ECM connectors. There does not appear to be a short circuit to other wires in the harness in the harness. Proceed to Test Step 5. Result: The continuity measurement did not indicate an open circuit. Repair: The wires with the low resistance reading to ground or to each other are damaged. Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the repair eliminates the problem. STOP |
| 5. Check the Start/Run/Stop Switch A. Ensure that the switch is not activated. B. Measure the resistance between the normally open terminals at the switch. C. Activate the switch. D. Measure the resistance between the normally open terminals at the switch. Note: The resistance measurement indicates an open circuit when the switch is in the STOP position. The resistance measurement indicates a short circuit when the switch is in the START position. E. Monitor the status of the ECS on Cat ET. The status for the ECS should indicate that the switch is in the OFF position. F. Short both jumper wires for the ECS to engine ground. G. Monitor the status of the ECS on Cat ET. The status for the ECS should indicate that the switch is in the ON position. |
ECS Status |
Result: The resistance measurement indicates an open circuit when the switch is in the STOP position. The resistance measurement indicates a short circuit when the switch is in the START position. The switch is OK. Proceed to Test Step 5. STOP Result: The resistance measurements are not correct. Repair: Replace the start/run/stop switch. Verify that the repair eliminates the problem. STOP |
| 5. Check for Proper Operation of the ECM A. Disconnect the J1/P1 ECM connector. B. Fabricate two jumper wires that are long enough to create a test circuit from the ECM connector to a good source of engine ground. Crimp connector sockets to one end of each of the jumper wires. C. Remove the wires from terminal locations P1-21 and P1-22. Install a jumper wire into each of these terminal locations at the ECM. Note: Ensure that the jumper wires are not touching any other wire and that the wires are insulated from engine ground. D. Monitor the status of the switch using Cat ET. The status for the switch should indicate that the switch is in the OFF position. E. Short both jumper wires to engine ground. F. Monitor the status of the switch using Cat ET. The status for the switch should indicate that the switch is in the ON position. |
ECS Status |
Result: Cat ET indicates the correct status for the switch. Repair: There may be an intermittent problem in the harness or in a connector. For information related to identifying intermittent electrical problems, refer to Troubleshooting, "Electrical Connectors - Inspect". STOP Result: Cat ET did not indicate the correct status for the ECS. There may be a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Test ECM Mode". Note: Before you consider replacing the ECM, consult with the Dealer Solutions Network (DSN) for assistance. STOP |
If the procedure did not correct the issue, contact your Cat Dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).
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