3500B and 3500C Locomotive Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the starting system or if one of the diagnostic codes in Table 1 is active.

The ECM can crank the engine when the start/run/stop switch is in the CLOSED position. When the engine is in the start up mode, the ECM will activate the prelube system. When the prelube cycle is finished, the ECM will begin the first crank cycle.

The crank cycle will continue for the time that is equal to the crank duration that has been programmed or the crank cycle will continue until the engine speed reaches the crank terminate speed. If crank terminate speed is not reached before the crank duration, the start enable relay will deactivate for a time that is equal to the cycle crank time.

This process will repeat for a programmed amount of times (Total Number of Crank Cycles). If the engine does not start the starter mode on the Caterpillar Electronic Technician (ET) will display "OVERCRANK". The engine control will be in an idle state.

Illustration 1	g01260749
Typical schematic

Illustration 2	g01259392
P2 ECM connector (P2-5) Digital return (P2-6) Start enable relay

Illustration 3	g01259393
P1 ECM connector (P1-21) Digital return (P1-22) Start/run/stop switch 3 (P1-70) Start/run/stop switch 4

Illustration 4	g01258378
Connector "F" (Terminal 2) −Battery (Terminal 6) +Battery

Illustration 5	g01234146
Location of ECM connectors

Illustration 6	g01259406
Connector "A" (Terminal 10) Start enable relay (Terminal 25) Digital return

Illustration 7	g01259410
Connector "G" (Terminal 1) Start enable relay (N/O) (Terminal 2) Start enable relay (COM)

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 FOR ACTIVE DIAGNOSTIC CODES FOR THE START ENABLE RELAY

1. Connect Cat ET to the service tool connector.

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

3. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

5. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active, but a problem is suspected in the starting system. Proceed to Test Step 6.

• Not OK - A -6 diagnostic code is active at this time. Proceed to Test Step 3.

• Not OK - A -5 diagnostic code is active at this time. Proceed to Test Step 4.

Test Step 3. CREATE AN OPEN AT THE START ENABLE RELAY

1. Disconnect the wires from terminal 3 on the start enable relay. Ensure that the wire is isolated from engine ground and other sources of electrical power.

2. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

4. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

Expected Result:

A -5 diagnostic code is now active for the start enable relay.

Results:

• OK - A -6 diagnostic code was active before disconnecting the wires. A -5 diagnostic code became active after disconnecting the wires. The harness and the ECM are OK. The problem may be in the start enable relay.

  Repair: Temporarily connect a new start enable relay, but do not install the new start enable relay. Verify that there are no active diagnostic codes for the start enable relay. If there are no active diagnostic codes for the start enable relay, permanently install the new start enable relay. Clear any logged diagnostic codes.

  STOP

• Not OK - A -6 diagnostic code remains active. There is a short between the start enable relay and the ECM. Leave the wires for the start enable relay disconnected. Proceed to Test Step 5.

Test Step 4. CREATE A SHORT AT THE CONNECTOR FOR THE START ENABLE RELAY

1. Install a jumper wire between terminal 4 and terminal 3 at the start enable relay.

2. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

4. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

Expected Result:

A -6 diagnostic code is active when the jumper wire is installed. A -5 diagnostic code is active when the jumper wire is removed.

Results:

• OK - A -6 diagnostic code is active when the jumper wire is installed. A -5 diagnostic code is active when the jumper wire is removed. The engine harness and the ECM are OK.

  Repair: Temporarily connect a new start enable relay, but do not install the new start enable relay. Verify that there are no active diagnostic codes for the start enable relay. If there are no active diagnostic codes for the start enable relay, permanently install the new start enable relay. Clear any logged diagnostic codes.

  STOP

• Not OK - The -5 diagnostic code remains active with the jumper in place. The open circuit is between the ECM and the start enable relay. Proceed to Test Step 5.

Test Step 5. TEST THE OPERATION OF THE ECM

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

2. Fabricate a jumper wire that can be used to replace the wire in the ECM connector for the start enable relay. Crimp a connector socket to one end of the jumper wire.

3. Disconnect the appropriate ECM connector for the start enable relay.

4. Remove the wire for the start enable relay from the ECM connector.

5. Install the jumper wire into the terminal location for the start enable relay at the ECM connector.

6. Connect the ECM connector.

7. Check the operation of the ECM by creating an open at the ECM:

   1. Hold the loose end of the jumper wire away from any components in order to create an open circuit condition.

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

   3. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

      Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

   5. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes for the start relay.

      Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

8. Check the operation of the ECM by creating a short circuit at the ECM:

   1. Short the jumper for the start enable relay to engine ground.

   2. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes for the start relay.

      Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

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

   4. Monitor the active diagnostic code screen on Cat ET. Check the starting system for an active diagnostic code.

      Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

9. Turn the start/run/stop switch to the STOP position. Return all wires to the original configuration.

Expected Result:

A -5 diagnostic code is active when the wire from the start enable relay is open at the ECM connector. A -6 diagnostic code is active if the wire from the start enable relay is shorted at the ECM connector.

Results:

• OK - The ECM is operating properly. The problem is in the wiring between the ECM and the connector for the start enable relay. Inspect the customer connector for damage or for a loose, corroded connection.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

• Not OK - One of the following conditions exists: The -5 diagnostic code is not active when the wire for the start enable relay is disconnected. The -6 diagnostic code is not active when the wire jumper is installed.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP

Test Step 6. CHECK THE NORMALLY OPEN CONTACTS ON THE START ENABLE RELAY

1. Remove the wires for the normally open contacts of the start enable relay from connector G. Refer to Illustration 1.

2. Connect a voltmeter between the wires that were removed in the above test step.

3. Measure the resistance between the wires that were removed in the previous test step.

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

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

6. Measure the resistance between the wires that were removed in the previous test step.

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

Expected Result:

The resistance measurement indicated an open circuit before the start enable relay was energized. The resistance measurement indicated a short circuit when the start enable relay was energized.

Results:

• OK - The resistance measurement indicated an open circuit before the start enable relay was energized. The resistance measurement indicated a short circuit when the start enable relay was energized.

  Repair: There may be a problem with the customer's wiring or with the customer's starting motor circuit. Refer to the "OEM Manual".

  STOP

• Not OK - The resistance measurement did not indicate an open circuit before the start enable relay was energized. The resistance measurement did not indicate a short circuit when the start enable relay was energized.

  Repair: The problem is in the wiring between the start enable relay and connector "G" or in the start enable relay.

  1. Remove the wires from the normally open contacts of the start enable relay.

  2. Connect a voltmeter between the contacts of the start enable relay. Measure the resistance between the normally open contacts of the start enable relay.

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

  4. Measure the resistance between the normally open contacts of the start enable relay.
  The resistance measurement indicated an open circuit before the start enable relay was energized. The resistance measurement indicated a short circuit when the start enable relay was energized. Repair the wiring between the start enable relay and connector G.

  The resistance measurement did not indicate an open circuit before the start enable relay was energized. The resistance measurement did not indicate a short circuit when the start enable relay was energized. Replace the start enable relay.

  STOP