C1.7 and C2.2 Industrial Engine Caterpillar

Relay - Test - Start Relay

Usage:

C1.7 G34

This procedure covers the following diagnostic codes:

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Table 1
Diagnostic Trouble Codes for the Start Relay
J1939 Code	Code Description	Comments
677-3	Starter Motor Relay : Voltage Above Normal	The Electronic Control Module (ECM) detects a high voltage condition (open circuit) in the start relay control circuit.
677-4	Starter Motor Relay : Voltage Below Normal	The Electronic Control Module (ECM) detects a low voltage condition (short circuit) in the start relay control circuit.
Follow the troubleshooting procedure to identify the root cause of the fault.

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Illustration 1	g06087955
Schematic for the start relay

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Illustration 2	g03836694

Note: When investigating a 677-4 code, disconnect the wires from the starting motor and insulate the wire terminals.

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Inspect the terminals on the start relay. Refer to Troubleshooting, "Electrical Connector - Inspect" for details. B. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors that are associated with the start relay. C. Check the harness for abrasion and pinch points from the start relay back to the ECMs.	Loose connection or damaged wire	Result: There is a fault in a connector or the wiring. Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all the seals are properly in place and ensure that the connectors are correctly coupled. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points. The fuses are not blown. Proceed to Test Step 2.
2. Check for Active Diagnostic Codes A. Connect the electronic service tool to the diagnostic connector. B. Turn the keyswitch to the ON position. Note: Do not start the engine. C. Use the electronic service tool to check for active diagnostic codes. D. Turn the keyswitch to the OFF position.	Diagnostic codes	Result: Diagnostic code 677-3 is active or recently logged. Proceed to Test Step 3. Result: Diagnostic code 677-4 is active or recently logged. Proceed to Test Step 6.
3. Check the Supply Voltage at the Start Relay Connector A. Remove the start relay. B. Turn the keyswitch to the START position. C. Measure the voltage between Test Point 1 on the relay socket and a suitable ground. D. Turn the keyswitch to the OFF position. E. Install the start relay.	At least 11 VDC	Result: The voltage is not within the expected range. Repair: Repair or replace the supply wiring to the start relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The voltage is within the expected range. Proceed to Test Step 4.
4. Check the Return Wire from the Start Relay to the Engine ECM A. Turn the keyswitch to the OFF position. B. Remove the start relay. C. Disconnect the P2 connector from the engine ECM. D. Measure the resistance between Test Point 2 on the start relay socket and P2:92. E. Connect the P2 connector to the engine ECM. F. Install the start relay.	Less than 2.0 Ohms	Result: The measured resistance is more than 2.0 Ohms. Repair: Repair or replace the return wiring from the start relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The measured resistance is less than 2.0 Ohms. Proceed to Test Step 5.
5. Check the Start Relay Solenoid for an Open Circuit A. Verify that the keyswitch is in the OFF position. B. Remove the start relay. C. Measure the resistance between Test Points 1 and 2 on the start relay. Refer to Illustration 2. D. Install the start relay.	81 Ohms to 113 Ohms	Result: The measured resistance is more than 81 Ohms to 133 Ohms. Repair: Install a replacement start relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The measured resistance is within 81 Ohms to 133 Ohms. Contact the Dealer Solutions Network (DSN).
6. Check the Wiring for a Short Circuit A. Turn the keyswitch to the OFF position. B. Remove the start relay. C. Disconnect the P2 connector from the engine ECM. D. Disconnect the P1 connector from the engine ECM. F. Check the resistance between P2:92 and all other pins on the P2 connector for the engine ECM. G. Check the resistance between P1:54 and all other pins on the P1 connector for the engine ECM. H. Reconnect the P1 connector to the machine ECM. I. Reconnect the P1 connector to the engine ECM. J. Reconnect the P2 connector to the engine ECM.	More than 1k Ohm	Result: One or more resistance measurements are less than 1k Ohm. Repair: Repair or replace the wiring. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All resistance measurements are more than 1k Ohm. Proceed to Test Step 7.
7. Check the Start Relay Solenoid for a Short Circuit A. Verify that the keyswitch is in the OFF position. B. Remove the start relay. C. Measure the resistance between Test Points 1 and 2 on the start relay. Refer to Illustration 2. D. Install the start relay.	81 Ohms to 113 Ohms	Result: The measured resistance is less than 81 Ohms to 133 Ohms. Repair: Install a replacement start relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The measured resistance is within 81 Ohms to 133 Ohms. Proceed to Test Step 8.
8. Perform a Start Relay Override Test A. Verify that the keyswitch is in the OFF position. B. Disconnect the wire from the starting motor solenoid. C. Turn the keyswitch to the ON position. D. Use the electronic service tool to perform the Start Relay Override Service Test. E. Measure the voltage between the starting motor solenoid wire and a suitable ground. F. Stop the Start Relay Override Service Test. G. Turn the keyswitch to the OFF position. H. Reconnect the wire to the starting motor solenoid.	Battery voltage	Result: The measured voltage is equal to battery voltage. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The measured voltage is not battery voltage. Contact the Dealer Solutions Network (DSN).