C7.1 Engines and Generator Sets Caterpillar

Glow Plug Starting Aid - Test

Usage:

C7.1 770

This procedure covers the following diagnostic code:

Use this procedure if there is a suspected fault in the glow plug start aid circuit or the glow plugs.

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Table 1
Diagnostic Trouble Codes For The Glow Plug Starting Aid
J1939 Code	CDL Code	Code Description	Comments
676-6	2246-6	Engine Glow Plug Relay : Current Above Normal	The Electronic Control Module (ECM) detects the following conditions: The engine is not cranking. The ECM has been powered for at least one second. There is a high current condition (short circuit) in the glow plug start aid relay circuit for more than 2 seconds. The warning light will come on. The diagnostic code will be logged. An ECM that was previously blank will require a total of 2 hours of operation before the diagnostic code will be logged. The ECM is unable to activate the relay for the glow plug starting aid. The glow plugs will not operate or the glow plugs will operate all the time. The engine may be difficult to start in cold temperatures and the exhaust may emit white smoke.
Follow the troubleshooting procedure to identify the root cause of the fault.

The following background information is related to this procedure:

The starting aid is used to improve engine starting when the engine is cold. With the keyswitch in the ON position, the ECM monitors the following parameters to decide if the glow plugs need to be switched ON:

Coolant temperature
Intake manifold air temperature

If the glow plugs are required, then the ECM will activate the starting aid relay for a controlled period. While the glow plug start aid relay is activated, the glow plug start aid relay will supply power to the glow plugs. If a "Wait To Start" lamp is installed, then this lamp will be illuminated to indicate the "Wait To Start" period.

"Wait to Start Lamp"

This feature may be included as an option.

When glow plugs need to be activated prior to starting, a lamp will indicate that the operator needs to "Wait to Start". Starting aids may be used during the cranking of the engine. Starting aids may be used if the engine has previously been started. The "Wait to Start" lamp will not be active in these conditions.

Electronic Service Tool Test Aid

The electronic service tool includes the test "Glow Plug Start Aid Override". This test will assist the analysis of the cold starting aid.

Overview of the Glow Plug Start Aid Override Test

The "Glow Plug Start Aid Override" test switches on the cold starting aid when the engine is not running.

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Illustration 1	g03788603
Schematic for the glow plug starting aid circuit. Not all connectors are shown. Refer to the electrical schematic for the application.

During the following procedure, refer to the electrical schematic for the application.

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. Check that the fuses are not blown. B. Inspect the terminals on the glow plug start aid relay and then inspect the connector on the flying lead from the relay. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Inspect the bus bar for the glow plugs. Ensure that the nuts that secure the bus bar to each glow plug are tightened to a torque of 2 N·m (17 lb in). Ensure that the bus bar is not shorted to the engine. D. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the glow plug starting aid. E. Check the screw for the ECM connector for the correct torque of 6 N·m (53 lb in). F. Check the harness for abrasion and pinch points from the glow plugs back to the ECM.	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. The bus bar is secured to the glow plugs and not shorted to ground. 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 select the "Glow Plug Start Aid Override Test" to turn on the power for the glow plugs. D. Check for active diagnostic codes or recently logged diagnostic codes.	Diagnostic codes	Result: No diagnostic codes are present. Repair: There may be an intermittent fault in an electrical component between the ECM and the glow plugs. The problem may be inside an electrical connector. Refer to Troubleshooting, "Electrical Connector - Inspect" to identify intermittent faults. There may be an open circuit in the relay circuit or there may be a fault in the glow plug switched power circuit. The ECM does not monitor the status of these conditions. Proceed to Test Step 3. Result: Diagnostic code 676-6 (2246-6) is active or recently logged. Proceed to Test Step 5.
3. Create a Short Circuit at the Relay Connector A. Turn the keyswitch to the OFF position. B. Remove the glow plug start aid relay. C. Fabricate a jumper wire. Install the jumper wire between Test Point 1 and Test Point 2 on the harness connector for the glow plug relay. Refer to Illustration 1. D. Turn the keyswitch to the ON position. E. Use the electronic service tool to select the "Glow Plug Start Aid Override Test"to turn on the power for the glow plugs. F. Use the electronic service tool to check for active diagnostic codes. Wait at least 30 seconds for activation of the diagnostic codes. G. Turn the keyswitch to the OFF position and remove the jumper wire.	Diagnostic code	Result: A 676-6 (2246-6) diagnostic code is active with the jumper installed. Repair: Install a replacement glow plug relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: There is no active diagnostic code. Proceed to Test Step 4.
4. Check the Wiring Between the ECM and the Relay for an Open Circuit A. Verify that the keyswitch is in the OFF position. B. Disconnect the P1 connector from the ECM. C. Inspect the P1 connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. D. Measure the resistance between Test Point 1 on the harness connector for the relay and the start aid control terminal on the P1 connector. E. Measure the resistance between Test Point 2 on the harness connector for the relay and the ground source. Refer to the electrical schematic for the application.	Less than 2.0 Ohms	Result: The resistance measurement is greater than 2.0 Ohms. The fault is in the wiring between the relay and the ECM. Repair: Repair the faulty wiring or replace the faulty wiring. Result: The resistance measurement is less than 2.0 Ohms. Proceed to Test Step 7.
5. Create an Open Circuit at the Relay A. Turn the keyswitch to the OFF position. B. Disconnect the glow plug start aid relay. C. Use the electronic service tool to select the "Glow Plug Start Aid Override Test" to turn on the power for the glow plugs. D. Use the electronic service tool to check for active diagnostic codes. Wait at least 30 seconds for activation of the diagnostic codes.	Diagnostic codes	Result: A 676-6 (2246-6) diagnostic code was previously active. There is no active diagnostic code with the relay disconnected. Repair: Install a replacement glow plug start aid relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The 676-6 (2246-6) diagnostic code is still active with the relay disconnected. Proceed to Test Step 6.
6. Check the Wiring Between the Relay and the ECM for a Short Circuit A. Disconnect the P1 connector. B. Inspect the P1 connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Measure the resistance between the start aid control terminal on the P1 connector and all other terminals on the P1 connector.	Greater than 100 Ohms	Result: At least one of the resistance measurements is less than 100 Ohms. There is a short in the wiring between the relay and the ECM. Repair: Repair the faulty wiring or replace the faulty 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 greater than 100 Ohms. Contact the Dealer Solutions Network (DSN).
7. Check the Operation of the Glow Plugs A. Place a suitable clamp-on ammeter on the power supply wire. B. Use the electronic service tool to select the "Glow Plug Start Aid Override Test" to turn on the power for the glow plugs. C. Wait for 20 seconds and then note the reading on the clamp-on ammeter.	Approximately 42.0 Amps for a 12 VDC system. Approximately 15.0 Amps for a 24 VDC system.	Result: The reading on the clamp on ammeter near the expected reading. The glow plugs are operating correctly. Return the engine to service. Result: The reading on the clamp on ammeter is between zero and the expected reading. Proceed to Test Step 8. Result: The reading on the clamp on ammeter is zero. Proceed to Test Step 9.
8. Test the Continuity of the Glow Plugs A. Disconnect the power supply and remove the bus bar from the glow plugs. B. Use a suitable digital multimeter to check continuity (resistance). Turn the audible signal on the digital multimeter ON. C. Place one probe on the connection for one of the glow plugs and the other probe to a suitable ground. The digital multimeter should make an audible sound. D. Repeat the continuity check on the remaining glow plugs.	One or more glow plugs do not have continuity.	Result: One or more of the glow plugs do not display continuity. Repair: Replace any glow plugs that do not show continuity. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All glow plugs display continuity. Contact the Dealer Solutions Network (DSN).
9. Check the Fuse A. Turn the battery disconnect switch to the OFF position. B. Check the fuse for the glow plug start aid relay. Refer to Illustration 1.	Blown fuse	Result: The fuse is blown - there is a short in the power circuit for the glow plugs. Check the wiring between the batteries and the glow plug relay for a short circuit. Refer to Illustration 1. Make any necessary repairs. Replace the blown fuse. Result: The fuse is not blown. Proceed to Test Step 10.
10. Check the Power Supply to the Relay Connector A. Disconnect the connector for the glow plug relay. B. Measure the voltage between Test Point A on the harness connector for the relay and a suitable ground. Refer to Illustration 1.	Battery voltage	Result: There is no battery voltage at Test Point A on the harness connector. Repair: Check all wiring between the batteries and the glow plug relay. Make any necessary repairs. Result: Battery voltage is present at Test Point A on the harness connector. Proceed to Test Step 11.
11. Check the Power Supply to the Glow Plugs A. Disconnect the power supply for the bus bar. Ensure that the glow plug relay is connected. B. Turn the keyswitch to the ON position. C. Use the electronic service tool to select the "Glow Plug Start Aid Override Test" to turn on the power for the glow plugs. D. Measure the voltage between the power supply wiring for the bus bar and engine ground.	Battery voltage	Result: There is no battery voltage at the power supply wiring to the bus bar. Repair: Check all wiring between the bus bar and the glow plug relay. Make any necessary repairs. If the wiring is OK, replace the glow plug relay. Result: Battery voltage is present at the power supply wiring to the bus bar. The glow plug circuit is operating correctly. Return the engine to service.