3500B and 3500C Locomotive Engines Caterpillar

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.

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	g01260749
Typical schematic

Illustration 2	g01259533
P1 ECM connector (P1-21) Start/Run/Stop switch 3 (P1-22) Start/Run/Stop switch 4

Illustration 3	g01259497
P2 ECM connector (P2-5) 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

1. Turn the breaker for the ECM to the OFF position.

2. Thoroughly inspect the ECM connectors. Inspect all of the other connectors for the circuit. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

4. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

5. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The connectors and wiring are OK. Proceed to Test Step 2.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. CHECK THE STATUS OF THE START/RUN/STOP SWITCH ON CATERPILLAR ELECTRONIC TECHNICIAN (ET)

1. Turn the breaker for the ECM to the ON position.

2. Connect Cat ET to the service tool connector.

3. Turn the start/run/stop switch to the STOP position.

4. Monitor the status for the start/run/stop switch on Cat ET.

5. Turn the start/run/stop switch to the START position.

6. Monitor the status for the start/run/stop switch on Cat ET.

7. Turn the start/run/stop switch to the STOP position.

Expected Result:

The status for the switch reads "OFF" when the start/run/stop switch is turned to the STOP position. The status for the switch reads "ON" when the start/run/stop switch is turned to the START position.

Results:

• OK - The status for the switch is correct in both the STOP and START positions.

  Repair: The switch is functioning correctly. Reset the system and check for any active diagnostic codes. If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The parameter for the switch is not correct in either the STOP position or in the START position. Proceed to Test Step 3.

Test Step 3. CHECK THE WIRING FOR AN OPEN CIRCUIT

1. Turn the breaker for the ECM to the OFF position.

2. Disconnect the ECM connector J1/P1.

3. Note the location of the wires on the start/run/stop switch. Remove the wires from the start/run/stop switch.

4. Install a wire jumper between the wire 998-BR(Brown) and the wires F716-WH(White) and F717-YL(Yellow) at the start/run/stop switch.

5. Measure the resistance between P1-21 and P1-5 at ECM connector P1.

6. Measure the resistance between P1-22 and P1-5 at ECM connector P1.

7. Remove the wire jumper.

Expected Result:

Each resistance measurement indicated a short circuit.

Results:

• OK - Each resistance measurement indicated a short circuit. Proceed to Test Step 4.

• Not OK - A resistance measurement did not indicate a short circuit.

  Repair: There is excessive resistance or an open in the wiring between the switch and the ECM connector P1. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 4. CHECK THE WIRING FOR A SHORT CIRCUIT

1. Ensure that the wires from the start/run/stop switch are not touching engine ground or any other wires in the harness.

2. Measure the resistance between P1-5 and every wire on the P1 connector. Measure the resistance between P1-5 and engine ground.

3. Measure the resistance between P1-21 and every wire on the P1 connector. Measure the resistance between P1-21 and engine ground.

4. Measure the resistance between P1-22 and every wire on the P1 connector. Measure the resistance between P1-22 and engine ground.

Expected Result:

Each resistance measurement indicated an open circuit.

Results:

• OK - Each resistance measurement indicated an open circuit. Proceed to Test Step 5.

• Not OK - A resistance 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.

  STOP

Test Step 5. CHECK THE START/RUN/STOP SWITCH

1. Ensure that the start/run/stop switch is not activated.

2. Measure the resistance between the normally open terminals on the start/run/stop switch.

3. Activate the start/run/stop switch.

4. Measure the resistance between the normally open terminals on the start/run/stop switch.

Expected Result:

The resistance measurement indicates an open circuit when the start/run/stop switch is in the STOP position. The resistance measurement indicates a short circuit when the start/run/stop switch is in the START position.

Results:

• OK - The resistance measurements are correct. Proceed to Test Step 6.

• Not OK - The resistance measurements are not correct.

  Repair: Replace the start/run/stop switch. Reconnect all connectors and wiring. Verify that the problem is no longer present.

  STOP

Test Step 6. CHECK THE ECM

1. Remove wire F716-WH(White) from the ECM connector P1-21. Install a wire jumper into the socket for P1-21.

2. Remove wire F717-YL(Yellow) from the ECM connector P1-22. Install a wire jumper into the socket for P1-22.

3. Reconnect the ECM connectors.

4. Turn the breaker for the ECM to the ON position.

5. Observe the status for the start/run/stop switch on Cat ET.

6. Short the wire jumpers from P1-21 and P1-22 to the digital return wire 998-BR(Brown) in P2-5.

7. Observe the status for the start/run/stop switch on Cat ET.

8. Turn the breaker for the ECM to the OFF position. Remove the wire jumpers. Reinstall all wires.

Expected Result:

The switch status reads "ON" when the wires are shorted to the digital return. The switch status reads "OFF" when the wires are not shorted to the digital return.

Results:

• OK - The parameter for the start/run/stop switch displays the proper state. The problem is not with the ECM.

  Repair: The ECM is receiving the correct signal input. The wiring is okay. The problem may be intermittent. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - The parameter for the start/run/stop switch does not show the correct state.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP