Use this procedure to troubleshoot the electrical system if a problem is suspected with the starting system. Also, use this procedure if one of the diagnostic codes in Table 1 is active.
| Diagnostic Codes Table | ||
|---|---|---|
| Description | Conditions which Generate this Code | System Response |
| 677-5 Engine Starter Motor Relay : Current Below Normal | The Electronic Control Module (ECM) detects an open circuit and/or a short to the +Battery in the circuit for the Starter Motor Magnetic Switch (SMMS). The ECM can only detect this condition when the SMMS is not energized. | The code is logged. |
| 677-6 Engine Starter Motor Relay : Current Above Normal | The ECM detects a short circuit to ground in the circuit for the SMMS. The ECM can only detect this condition when the SMMS is energized. | |
The engine control system controls all aspects of engine start and stop functionality. In order to crank the engine, the ECM sends a signal to the Starting Motor Magnetic Switch (SMMS). Current will flow to the starting motor through the contacts of the SMMS. The starting motor will begin to crank the engine.
The ECM receives a request to crank the engine over the CAN data link from the Electronic Modular Control Panel 3 (EMCP). Ensure that the "Engine State Control Input Configuration" is configured to "CAN Input" if an EMCP is installed on the engine.
If the "Engine State Control Input Configuration" parameter is configured to "Hardwired", a switch input will be used by the ECM for engine starting. The switch must be wired to terminal location 40 at the J1/P1 ECM connector. Table defines the functionality of the switch input.
| ECM Switch Input | Switch Input | Engine State |
| P1/J1-40 | −Battery | Start/Run |
| P1/J1-40 | +Battery | Stop |
Refer to Troubleshooting, "Configuration Parameters".
The ECM will crank the engine until the programmed "Crank Terminate RPM" has been reached. If the engine fails to reach the "Crank Terminate RPM" before the programmed "Crank Duration" period, the ECM will stop cranking the engine. The ECM will then allow the starter to cool for a period that is equal to the "Crank Duration" before starting the next crank cycle. The process will be repeated for a number of times that is equal to the programmed "Maximum Number of Crank Cycles". When the "Maximum Number of Crank Cycles" has been reached, the process will be aborted and Caterpillar Electronic Technician (ET) will display "OVERCRANK". The process will be restarted when the next start request is received by the ECM.
Refer to Troubleshooting, "Configuration Parameters" for the available ranges and default settings of the following parameters:
- "Crank Duration"
- "Crank Terminate RPM"
- "Maximum Number of Crank Cycles"
Note: If the "Crank Duration" or "Maximum Number of Crank Cycles" are programmed to 0, the ECM will not crank the engine.
| |
| Illustration 1 | g02175710 |
|
Schematic for the starting circuit | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Remove electrical power from the ECM.
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Illustration 2 g02164341 Location of ECM connectors
(1) P1/J1 - Thoroughly inspect the ECM connectors. Inspect all of the other connectors for the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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Illustration 3 g02175714 Terminal locations at the P1 ECM connector for the starting circuit
(43) SMMS driver
(51) SMMS driver - 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 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 coupled.
Verify that the repair eliminates the problem.
STOP
Test Step 2. Check for Active Diagnostic Codes for the SMMS
- Connect Cat ET to the service tool connector.
- Restore electrical power to the ECM.
- Monitor the active diagnostic code screen on Cat ET. Check for an active -5 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Monitor the active diagnostic code screen on Cat ET. Check for a -6 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Deactivate the override for the starting system.
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 Coil of the SMMS
- Disconnect the wires from terminal 1 and terminal 2 on the SMMS or disconnect the connectors for the SMMS, if equipped. Ensure that the wires are isolated from engine ground and from sources of electrical power.
- Monitor the active diagnostic code screen on Cat ET. Check for a -5 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Monitor the active diagnostic code screen on Cat ET. Check for a -6 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Deactivate the override for the starting system.
Expected Result:
A -5 diagnostic code is now active for the starting motor system.
Results:
- OK - A -5 diagnostic code became active after creating the open at the SMMS. The wires from the ECM to the SMMS are OK.
Repair: The problem may be in the coil of the SMMS. Install a new SMMS. Clear any logged diagnostic codes.
STOP
- Not OK - A -6 diagnostic code remains active. There is a short between the SMMS and the ECM. Leave the wires for the SMMS disconnected. Proceed to Test Step 5.
Test Step 4. Create a Short at the Coil of the SMMS
- Install a jumper wire between terminal 1 and terminal 2 at the SMMS.
- Monitor the active diagnostic code screen on Cat ET. Check for a -5 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Monitor the active diagnostic code screen on Cat ET. Check for a -6 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Deactivate the override for the starting system.
Expected Result:
A -6 diagnostic code is active when the jumper wire is installed.
Results:
- OK - A -6 diagnostic code is active when the jumper wire is installed. The wires from the ECM to the SMMS are OK.
Repair: The problem may be in the coil of the SMMS. Install a new SMMS. Clear any logged diagnostic codes.
STOP
- Not OK - The -5 diagnostic code is active when the sourcing driver for the SMMS is not activated. A -6 code does not activate when the override for the starting system is activated with the jumper in place. The open circuit is between the ECM and the SMMS. Proceed to Test Step 5.
Test Step 5. Test the Operation of the ECM
- Fabricate a jumper wire that can be used to replace the wire in the ECM connector for the SMMS. Crimp a connector socket to one end of the jumper wire.
- Turn the main disconnect switch to the OFF position.
- Disconnect the appropriate ECM connector for the SMMS.
- Remove the wire for the SMMS from the ECM connector.
- Install the jumper wire into the terminal location for the SMMS at the ECM connector.
- Connect the ECM connector.
- Check the operation of the ECM by creating an open at the ECM:
- Hold the loose end of the jumper wire away from any components in order to create an open circuit condition.
- Turn the main disconnect switch to the ON position.
- Monitor the active diagnostic code screen on Cat ET. Check for a -5 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic code to become active.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Monitor the active diagnostic code screen on Cat ET. Check for a -6 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic code to become active.
- Deactivate the override for the starting system.
- Check the operation of the ECM by creating a short circuit at the ECM:
- Short the jumper wire for the SMMS to engine ground.
- Monitor the active diagnostic code screen on Cat ET. Check for a -5 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic code to become active.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Monitor the active diagnostic code screen on Cat ET. Check for a -6 diagnostic code for the SMMS.
Note: Wait at least 30 seconds in order for the diagnostic code to become active.
- Deactivate the override for the starting system.
- Remove electrical power from the ECM. Reconnect all wires to the original configuration.
Expected Result:
A -5 diagnostic code is active when the wire for the SMMS is open at the ECM connector. A -6 diagnostic code is active when the wire for the SMMS is shorted at the ECM connector.
Results:
- OK - The ECM is operating properly. The problem is in the wiring between the ECM and the SMMS.
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 SMMS is disconnected. The -6 diagnostic code is not active when the wire jumper is installed.
Repair: There appears to be a problem with the ECM. Before you consider replacing the ECM, consult the Dealer Solution Network (DSN). Verify that the original problem is resolved.
STOP
Test Step 6. Check the Voltage at the Plus Battery Side of the Normally Open Contacts of the SMMS
- Measure the voltage between terminal 4 of the SMMS and engine ground.
Expected Result:
The voltage measures 24 ± 3 VDC.
Results:
- OK - The voltage measures 24 ± 3 VDC. Proceed to Test Step 7.
- Not OK - The voltage does not measure 24 ± 3 VDC.
Repair: The problem appears to be in the wiring between the +Battery terminal and the SMMS. Verify that any breaker between the SMMS and the +Battery terminal is not tripped. Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 7. Check the Voltage from the SMMS to the Starting Motor
- Remove the wire from terminal 3 of the SMMS.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Measure the voltage between terminal 3 on the SMMS and engine ground while the override is active.
- Deactivate the override for the starting system.
- Restore the wiring to the original configuration.
Expected Result:
The voltage measures 24 ± 3 VDC.
Results:
- OK - The voltage measures 24 ± 3 VDC. Proceed to Test Step 8.
- Not OK - The voltage does not measure 24 ± 3 VDC.
Repair: Voltage is present at the normally open contacts of the SMMS. There are no diagnostic codes for the SMMS. Voltage is not present on the wire going to the starting motors. Replace the SMMS.
STOP
Test Step 8. Check the Voltage at the Starting Motors
- Disconnect the wire that leads from terminal 3 of the SMMS at the starter solenoid.
- Proceed to the "Diagnostic Overrides" screen on Cat ET. Activate the override for the starting system.
- Measure the voltage between the wire from the SMMS and the engine ground.
- Deactivate the override for the starting system.
- Restore the wiring to the original configuration.
Expected Result:
The voltage measures 24 ± 3 VDC.
Results:
- OK - The voltage measures 24 ± 3 VDC. The problem appears to be in the starting motor solenoid.
Repair: Verify that you have continuity on the return wire for the starting motor solenoid between terminal G and the −Battery. If the return wire for the starting motor solenoid is OK, verify that you have continuity on the +Battery wire for the starting motor solenoid between terminal +Batt and the +Battery. If the wires to the starting motor solenoid are OK, Install a new starting motor solenoid.
STOP
- Not OK - The voltage does not measure 24 ± 3 VDC. The problem is in the wiring between the SMMS and the starting motor solenoid.
Repair: Repair the wiring.
STOP