3512C Engine for Caterpillar Built Machines 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 has the ability to crank the engine when the "Start/Run/Stop" switch is turned to the START/RUN position. The crank cycle will continue for the time that is equal to the cycle crank time 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 cycle crank time, the drive 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 start-up mode on Caterpillar Electronic Technician (ET) will display "OVERCRANK". The engine control will be in an idle state.

When the "Start/Run/Stop" switch is turned to the START/RUN position the "Start Deck Engine Relay (SDER)" is energized by the master "DCU". A set of normally open contacts on the "SDER" close. This changes the start/run/stop inputs to the ECM from a floating state to a low state. The ECM recognizes the low state on these inputs as a start signal. The ECM then energizes the "Start Relay" through the "Crank Relay Drive" output. A set of normally open contacts from the "Start Relay" close energizing the "Start Deck Engine Solenoid (SDES)". Refer to Illustration 1.

Illustration 1	g01286693
Typical example

Illustration 2	g01287186
P2 ECM connector (P2-6) "Crank relay drive" (P2-7) "Crank relay return"

Illustration 3	g01285750
Location of ECM connectors

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the "main disconnect switch (MDS)" 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 Relay

1. Connect Cat ET to the service tool connector.

2. Turn the "MDS" 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/RUN 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 the "start deck engine solenoid" is not energizing. 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 Relay

1. Disconnect the wire from terminal A1 on the start relay. Ensure that the wire is isolated from engine ground and other sources of electrical power.

2. Turn the "MDS" 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/RUN 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:

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

Results:

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

  Repair: Temporarily connect a new start relay. Verify that there are no active diagnostic codes for the start relay. If there are no active diagnostic codes for the start relay, permanently install the new start relay. Clear any logged diagnostic codes.

  STOP

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

Test Step 4. Create a Short at the Start Relay

1. Install a jumper wire between terminal A1 and terminal A2 at the start 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/RUN 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 relay. Verify that there are no active diagnostic codes for the start relay. If there are no active diagnostic codes for the start relay, permanently install the new start 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 relay. Proceed to Test Step 5.

Test Step 5. Test the Operation of the ECM

1. Turn the "MDS" to the OFF position.

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

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

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

5. Install the jumper wire into the terminal location for the start 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 "MDS" 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/RUN 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 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/RUN 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 relay is open at the ECM connector. A -6 diagnostic code is active if the wire from the start 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 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 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 Voltage from the Normally Open Contacts of the Start Relay

1. Remove the wire from terminal 14 of the start relay.

2. Connect a voltmeter between terminal 14 and engine ground.

3. Turn the "fuel cutoff switch" on the main junction box to the OFF position.

4. Turn the "MDS" to the ON position.

5. Monitor the voltage reading on the voltmeter.

6. Turn the "MDS" to the OFF position.

7. Replace all wires to the original configuration.

Expected Result:

The voltage measures 12 ± 1 VDC.

Results:

• OK - The voltage measures 12 ± 1 VDC. Proceed to Test Step 7.

• Not OK - The voltage does not measure 12 ± 1 VDC.

  Repair: The problem is between the start relay and the Battery. Perform the following steps.

  1. Turn the "MDS" to the ON position.

  2. Measure the voltage at the following test points.
     • Terminal T1 on the "MDS"

     • Terminal 1A

     • TB-4

     • Terminal 11 on the start relay

  The voltage should measure 12 ± 1 VDC at each test point. If voltage is not measured at a test point, the problem is in the circuit that precedes that test point.

  STOP

Test Step 7. Check the Voltage to the "Start Deck Engine Solenoid (SDES)"

1. Remove the wire from terminal TB-31 that goes to the "start deck engine solenoid". Refer to Illustration 1.

2. Connect a voltmeter between terminal TB-31 and engine ground.

3. Turn the "fuel cutoff switch" on the main junction box to the OFF position.

4. Turn the "MDS" to the ON position.

5. Monitor the voltage reading on the voltmeter.

6. Turn the "MDS" to the OFF position.

7. Replace all wires to the original configuration.

Expected Result:

The voltage measures 12 ± 1 VDC.

Results:

• OK - The voltage measures 12 ± 1 VDC.

  Repair: Check continuity between the wire on terminal TB-31 and the "Start Deck Engine Solenoid". Check continuity between the wire on terminal TB-2 and the "Start Deck Engine Solenoid". If the wires are okay, replace the "Start Deck Engine Solenoid". Verify that the system is working correctly.

  STOP

• Not OK - The voltage does not measure 12 ± 1 VDC.

  Repair: There is a problem in the wiring and/or connectors between terminal 14 of the start relay and terminal TB-31. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP