C1.7 and C2.2 Industrial Engine Caterpillar

Glow Plug Starting Aid - Test

Usage:

C1.7 G34

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	Code Description	Comments
676-3	Engine Glow Plug Relay : Voltage 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 voltage condition (open 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. The ECM is unable to activate the relay for the glow plug starting aid. The glow plugs will not operate. The engine may be difficult to start in cold temperatures and the exhaust may emit white smoke.
676-4	Engine Glow Plug Relay : Voltage Below 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 low voltage 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. 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 the 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
Fuel temperature

If the glow plugs are required, then the ECM will activate the starting aid relay for a controlled period. When 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"

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 Test". This test will assist the analysis of the cold starting aid.

Overview of the Glow Plug Start Aid Override Test

This glow plug start aid override test switches on the cold starting aid when the engine is not running. The glow plug start aid override test aids the analysis of the circuit for the glow plug start aid relay.

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Illustration 1	g06100705
Schematic for the glow plug starting aid circuit

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Illustration 2	g06036121
Pin locations on the P2 connector for the glow plug starting aid circuit (90) Glow plug start aid control

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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 on 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 wire in the ECM connector that is associated with the glow plug starting aid. E. 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 a fault in the glow plug switched power circuit. The ECM does not monitor the status of this condition. Proceed to Test Step 7 to test this circuit. Result: Diagnostic code 676-3 is active or recently logged. Proceed to Test Step 3. Result: Diagnostic code 676-4 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 676-3 diagnostic code was previously active. A 676-4 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: The 676-3 diagnostic code is still active. 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 P2 connector from the ECM. C. Inspect the P2 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 P2:90. E. Measure the resistance between Test Point 2 on the harness connector for the relay and engine ground.	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 676-4 diagnostic code was previously active. A 676-3 diagnostic code is active 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 676-4 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 P2 connector. B. Inspect the P2 connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Use a suitable multimeter to measure the resistance between P2:90 and all other terminals on the P2 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 7 seconds and then note the reading on the clamp-on ammeter.	Approximately 21.0 Amps for a 3 cylinder engine. Approximately 28.0 Amps for a 4 cylinder engine.	Result: The reading on the clamp on ammeter is 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. Repeat this procedure from Test Step 1.
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. Do not replace the fuse at the stage. Proceed to Test Step 10. Result: The fuse is not blown - there may be an open circuit in the power circuit for the glow plugs. Proceed to Test Step 12.
10. Disconnect the Relay and Check the Fuse A. Disconnect the glow plug start aid relay. B. Replace the fuse for the relay. C. Turn the battery disconnect switch to the ON position. Wait for 5 seconds. D. Turn the battery disconnect switch to the OFF position. E. Check the fuse.	Blown fuse	Result: The fuse is blown - there is a short circuit in the wiring between the fuse and the glow plug start aid relay. Repair: Repair the faulty wiring or replace the faulty wiring. Replace the fuse and reconnect the relay. Turn the battery disconnect switch to the ON position. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The fuse is not blown. Proceed to Test Step 11.
11. Check the Wiring Between the Relay and the Bus Bar for a Short Circuit A. Disconnect the power supply wire from the bus bar. B. Measure the resistance between Test Point B on the harness connector for the relay to a suitable engine ground.	Greater than 10000 Ohms	Result: The resistance is greater than 10000 Ohms. Repair: Install a replacement relay. Reconnect the power supply wire to the bus bar. Turn the battery disconnect switch to the ON position. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The resistance is less than 10000 Ohms. There is a short in the wiring between the relay and the bus bar. Repair the faulty wiring or replace the faulty wiring. Turn the battery disconnect switch to the ON position. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.
12. Check the Input Voltage to the Relay A. Disconnect the connector for the glow plug start aid relay. B. Turn the battery disconnect switch to the ON position. C. Measure the voltage at Test Point A on the harness connector for the relay to a suitable ground.	At least 11 VDC	Result: The voltage is not as expected. The fault is in the wiring between the battery and the relay. Repair: Repair the faulty wiring or replace the faulty wiring. Reconnect the relay. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The voltage is as expected. Leave the relay disconnected and proceed to Test Step 13.
13. Bypass the Relay A. Turn the battery disconnect switch to the OFF position. B. Fabricate an 8 AWG jumper wire that is 150 mm (6 inch) long. C. Install the jumper wire between Test Point A and Test Point B on the harness connector for the relay. D. Turn the battery disconnect switch to the ON position. E. Use a clamp-on ammeter to measure the current on the power supply wire to the glow plugs. F. Turn the battery disconnect switch to the OFF position. G. Remove the jumper.	Approximately 21.0 Amps for a 3 cylinder engine. Approximately 28.0 Amps for a 4 cylinder engine.	Result: The reading on the clamp-on ammeter is correct. Repair: Install a replacement relay. Turn the battery disconnect switch to the ON position. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The reading on the clamp-on ammeter is zero. The fault is in the wiring between the relay and the bus bar. Repair: Repair the faulty wiring or replace the faulty wiring. Turn the battery disconnect switch to the ON position. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. If the procedure did not correct the issue, contact the Dealer Solutions Network (DSN).