G3306B Petroleum Generator Set Engines Caterpillar

Use this procedure to troubleshoot a suspected problem with the engine starting system. Also, use this procedure if one of the diagnostic codes in Table 1 are active or easily repeated.

Table 1

Diagnostic Codes Table
Code and 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 in the circuit for the start control relay for more than 5 seconds. The output driver must be off in order for this code to become active.	The code is logged. The amber warning lamp is illuminated.
677-6 Engine Starter Motor Relay : Current Above Normal	The ECM detects a short in the circuit for the start control relay for more than 5 seconds. The output driver must be on in order for this code to become active.	The code is logged. The amber warning lamp is illuminated.

The engine ECM contains the logic and the outputs for starting the engine. The logic for starting the engine is customer programmable. The logic responds to inputs from the following components: engine control switch, emergency stop switch, remote start switch, data link and other inputs.

The ECM also has outputs that are used for communicating the current state of engine operation. One of the outputs sends a signal to indicate that the crank terminate speed has been achieved. Another output sends a signal that indicates that the engine is running. Both of these outputs are low side ECM drivers. The power for the circuits is provided at the electrical component and the ground circuit is provided by the ECM. Refer to Troubleshooting, "Indicator Lamp - Test" for information that is related to troubleshooting these circuits.

The most likely causes of any of these diagnostic codes are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with one of the solenoids that are related to the code. The least likely cause is a problem with the ECM.

The ECM supplies +Battery voltage to the start control relay when the logic determines the necessity. The ECM removes the voltage when the crank terminate speed has been achieved. Also, if the timer for the "Cycle Crank Time" parameter is exceeded, voltage will be removed from the start control relay.

Illustration 1	g02025907
Schematic for the components of the engine starting system

Illustration 2	g02029068
Location of the components for the engine starting system (right side engine view) (1) J2/P2 ECM connectors (2) Electric start control (start control relay)

Illustration 3	g01413257
Location of the connector for the air start control (right rear engine view) (3) Harness connector for the air start control (start control relay)

Illustration 4	g02029132
Terminal locations at the P2 ECM connector that are associated with the starting system (P2-17) Starting motor output (P2-19) Return

Illustration 5	g01155187
Terminal locations at the harness connector for the start control relay (1) Start control relay (2) Return

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Set the engine control switch to the OFF position. Remove the electrical power from the engine. B. Thoroughly inspect ECM connectors (1) . Also, thoroughly inspect the other components for the starter circuit that is for your application. Refer to Testing and Adjusting, "Electrical Connectors - Inspect" for details. C. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the engine starting system. D. Check the fastener for each of the ECM connectors for the proper torque. Refer to Testing and Adjusting, "Electrical Connectors - Inspect" for the correct torque values. E. Check the wiring harnesses for abrasion, for corrosion and for pinch points.	Damaged Connector or wiring	Result: The harness and wiring appear to be OK. Proceed to Test Step 2. Result: There is a problem in the wiring harness. Repair the connectors and/or the wiring. Replace parts, if necessary. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the problem is resolved.
2. Check for Active Diagnostic Codes A. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. B. Connect Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools". C. Restore the electrical power to the engine. Turn the engine control to the STOP position. Note: The 677-5 Engine Starter Motor Relay : Current Below Normal can only be detected when the output for the start command is off. The output is normally off when the engine control switch is in the STOP position. The output is also off when the output for the crank terminate relay is activated. D. Turn the engine control to the START position. Attempt to start the engine. Note: The 677-6Engine Starter Motor Relay : Current Above Normal can only be detected when the output for the start command is on. The output is normally on when the engine control is switched from the STOP position to the START position. The output remains on during engine cranking. E. Turn the engine control to the STOP position.	Active Diagnostic codes	Result: No diagnostic codes were activated. The output for the starting system appears to be OK. The initial diagnostic code was probably caused by a poor electrical connection. If an intermittent electrical problem is suspected, refer to Testing and Adjusting, "Electrical Connectors - Inspect", for information that is related to troubleshooting intermittent electrical problems. Result: A 677-5 diagnostic code was activated during the test. This code can be caused by an actual open circuit or by a short circuit to the +Battery side. Proceed to Test Step 3. Result: After the engine was cranked, a 677-6 diagnostic code was activated. There is a short circuit in the harness or in the solenoid. Proceed to Test Step 7.

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Gaseous fuel is present. Personal Injury or Death can result from an open flame or spark igniting the gaseous fuel causing an explosion and/or fire. Always use a gas detector to determine the presence of gaseous fuel when maintaining and servicing. Contact your local gas provider immediately for assistance in the event of a leak.

Table 3

Troubleshooting Test Steps	Values	Results
3. Check for a Short Circuit to the +Battery in the Harness Note: Open sparks may be generated during this test. A. Ensure that no combustible gas is present in the surrounding atmosphere. B. Verify that the engine control switch is in the STOP position. C. Disconnect the connector from the start control relay. D. Use a multimeter to check the voltage at the harness connector for the start control relay.	Short circuit	Result: Voltage is not present at the harness connector for the start control relay. There is no short circuit to the +Battery in the harness. There may be an open circuit in the harness. Proceed to Test Step 4. Result: Voltage is present at the harness connector for the start control relay while the engine control switch is in the STOP position. The solenoid is receiving power when the engine control switch is in the STOP position. Proceed to Test Step 6.
4. Create a Short Circuit at the Harness Connector for the Start Control Relay A. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. B. Fabricate a jumper wire that is long enough to create a test circuit at the harness connector for the starter. Crimp connector pins to each end of the jumper wire. C. Disconnect the harness connector from the start control relay. D. Install the jumper wire into the two terminals of the harness connector for the start control relay. E. Restore the electrical power to the engine. Turn the engine control switch to the STOP position. The 677-5 Engine Starter Motor Relay : Current Below Normal can only be detected when the output for the start command is off. The output is normally off when the engine control switch is in the STOP position. The output is also off when the output for the crank terminate relay is activated. Monitor the active diagnostic code and the logged diagnostic codes on Cat ET. Wait at least 30 seconds in order for diagnostic codes to become active. F. Turn the engine control switch to the OFF position. Remove the electrical power from the engine.	Active Diagnostic codes	Result: A 677-5 diagnostic code was not activated when the jumper wire was installed. The ECM detected the short circuit that was created by the jumper wire. There appears to be an open circuit in the start control relay. Perform the following procedure: 1. Disconnect the harness connector for the start control relay. 2. Use a multimeter to measure the resistance of the coil that is for the start control relay. Check the resistance between terminals 1 and 2 at the harness connector for the start control relay. 3. Restore the wiring to the original configuration. For an electric start control, the correct resistance of the coil is 27.5 Ohms with the coil at 25.5 °C (78 °F). For an air start control, the correct resistance of the coil is 16.5 Ohms with the coil at 25.5 °C (78 °F). If the condition of the coil is suspect, replace the start control relay. Verify that the original condition is resolved. Result: A 677-5 diagnostic code was activated when the jumper wire was installed. The ECM did not detect the short circuit. Proceed to Test Step 5.
5. Check for Proper Operation of the ECM A. Verify that the engine control switch is in the OFF position and that the electrical power is removed from the engine. B. Disconnect the J2/P2 ECM connectors. C. Fabricate a jumper wire that is long enough to create a test circuit across the ECM connector. Crimp connector sockets to each end of the jumper wire. D. Remove the wires from terminal locations P2-17 and P2-19 at the ECM connector. Install one end of the jumper wire into each of these terminal locations. E. Connect the J2/P2 ECM connectors. F. Restore the electrical power to the engine. Turn the engine control switch to the STOP position. The 677-5Engine Starter Motor Relay : Current Below Normal can only be detected when the output for the start command is off. The output is normally off when the engine control switch is in the STOP position. The output is also off when the output for the crank terminate relay is activated. Monitor the active diagnostic code and the logged diagnostic codes on Cat ET. Wait at least 30 seconds in order for diagnostic codes to become active. G. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. H. Restore the wiring to the original configuration.	677-5	Result: The ECM did not detect the jumper wire that was installed at the P2 ECM connector. There appears to be a problem with the ECM. Perform the following procedure: 1. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. 2. Temporarily install a new ECM. Refer to Testing and Adjusting, "ECM - Replace" for details. If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Result: When the jumper wire was installed, the 677-5 diagnostic code was activated. The ECM did not detect the jumper wire that was installed at the solenoid connector. The ECM did detect the jumper wire that was installed at the P2 ECM connector. There is an open circuit in the wiring harness between the ECM connector and the harness connector that is for the start control relay. Repair the wiring. Verify that the repair resolves the original problem.
6. Check for a Short Circuit to the +Battery at the ECM A. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. B. Disconnect the J2/P2 ECM connectors. C. Fabricate two jumper wires that are long enough to create test circuits at the ECM connector. Crimp connector sockets to one end of each of the jumper wires. D. Remove the wires from terminal locations P2-17 and P2-19 at the ECM connector. Install a jumper wire into each of these terminal locations. E. Connect the J2/P2 ECM connectors. F. Restore the electrical power to the engine. Turn the engine control switch to the STOP position. G. With the engine control switch in the STOP position, use a multimeter to measure the voltage between jumper wires at the ECM. H. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. I. Restore the wiring to the original configuration.	Short Circuit	Result: With the engine control switch in the STOP position, a voltage is not present at the test circuit across the ECM connector. There is a short circuit to battery voltage in the harness between the P2 ECM connector and the harness connector for the start control relay. Repair the harness, when possible. Replace parts, if necessary. Result: When the engine control switch is in the STOP position, 18 to 28.5 VDC is present at the ECM connector. There appears to be a problem with the ECM. Perform the following procedure: 1. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. 2. Temporarily install a new ECM. Refer to Testing and Adjusting, "ECM - Replace" for details. If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM.
7. Check for a Short Circuit to the +Battery at the ECM A. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. B. Disconnect the harness connector from the start control relay. C. Restore the electrical power to the engine. Turn the engine control switch to the STOP position. D. Turn the engine control switch to the START position for at least 10 seconds. Then turn the engine control switch to the STOP position. The 677-6Engine Starter Motor Relay : Current Above Normal can only be detected when the output for the start command is on. The output is normally on when the engine control switch is switched from the STOP position to the START position. The output remains on during engine cranking. E. Use Cat ET to look for an active 677-6 diagnostic code.	Open Circuit	Result: A 677-6 diagnostic code was not activated during the attempt to start the engine. There appears to be a short circuit in the start control relay. Perform the following procedure: 1. Disconnect the harness connector for the start control relay. 2. Use a multimeter to measure the resistance of the coil that is for the start control relay. Check the resistance between terminals 1 and 2 at the connector for the start control relay. 3. Restore the wiring to the original configuration. For an electric start control, the correct resistance of the coil is 27.5 Ohms with the coil at 25.5 °C (78 °F). For an air start control, the correct resistance of the coil is 16.5 Ohms with the coil at 25.5 °C (78 °F). If the condition of the coil is suspect, replace the start control relay. Verify that the original condition is resolved. Result: A 677-6 diagnostic code was activated when the start control relay was disconnected. The start control relay is OK. The short circuit is in the harness or in a connector. There may be a problem with the ECM. Proceed to Test Step 8.

Table 4

Troubleshooting Test Steps	Values	Results
8. Check for Proper Operation of the ECM A. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. B. Disconnect the J2/P2 ECM connectors. C. Remove the wires from terminal locations P2-17 and P2-19 at the ECM connector. D. Connect the J2/P2 ECM connectors. E. Restore the electrical power to the engine. Turn the engine control switch to the STOP position. F. Turn the engine control switch to the START position for at least 10 seconds. Then turn the engine control switch to the STOP position. The 677-6Engine Starter Motor Relay : Current Above Normal can only be detected when the output for the start command is on. The output is normally on when the engine control switch is switched from the STOP position to the START position. The output remains on during engine cranking. G. Use Cat ET to look for an active 677-6 diagnostic code. H. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. I. Restore the wiring to the original configuration.	677-6	Result: When the wiring was disconnected from the ECM, a 677-6 diagnostic code was not activated. There is a problem with the wiring that is between the ECM connector and the harness connector that is for the start control relay. Repair the wiring. Verify that the repair resolves the original problem. Result: When the wiring was disconnected from the ECM, a 677-6 diagnostic code was activated. There appears to be a problem with the ECM. Perform the following procedure: 1. Turn the engine control switch to the OFF position. Remove the electrical power from the engine. 2. Temporarily install a new ECM. Refer to Testing and Adjusting, "ECM - Replace" for details. If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM.