C3.4B Engines Glow Plug Starting Aid - Test Caterpillar


Glow Plug Starting Aid - Test
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This procedure covers the following diagnostic codes:

Table 1
Diagnostic Trouble Codes for the Glow Plug Start Aid Circuit 
J1939 Code  Description  Notes 
676-5  Engine Glow Plug Relay : Current Below Normal  The Electronic Control Module (ECM) detects a low current condition in the control circuit for the Glow plug Control Unit (GCU) for at least 0.7 seconds.
The warning lamp will come on. 
676-6  Engine Glow Plug Relay : Current Above Normal  The ECM detects a high current condition in the control circuit for the GCU for at least 0.2 seconds.
The ECM will attempt to activate the glow plug control unit for a further five attempts after the diagnostic code becomes active.
The warning lamp will come on. 
676-19  Engine Glow Plug Relay : Data Error  The ECM detects one of the following conditions:
The diagnostic signal from the GCU indicates that there is an error in the GCU.
OR
The diagnostic signal from the GCU is invalid.
The warning lamp will come on. 
5324-7  Engine Glow Plug 1 : Not Responding Properly  The ECM detects the following conditions:

The diagnostic signal from the GCU indicates that there is a short in the circuit for the glow plug for cylinder number 1.
 
5325-7  Engine Glow Plug 2 : Not Responding Properly  The ECM detects the following conditions:

The diagnostic signal from the GCU indicates that there is a short in the circuit for the glow plug for cylinder number 2.
 
5326-7  Engine Glow Plug 3 : Not Responding Properly  The ECM detects the following conditions:

The diagnostic signal from the GCU indicates that there is a short in the circuit for the glow plug for cylinder number 3.
 
5327-7  Engine Glow Plug 4 : Not Responding Properly  The ECM detects the following conditions:

The diagnostic signal from the GCU indicates that there is a short in the circuit for the glow plug for cylinder number 4.
 

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 Electronic Control Module (ECM) will monitor the coolant temperature and the engine air inlet temperature in order to decide if the glow plugs need to be switched ON. If the glow plugs are required, then the ECM will activate the glow plug control unit for a controlled period. While the glow plug control unit is activated, the glow plug control unit will supply power to the glow plugs.

Glow plugs are used for temperatures that are below 5° C (41° F).

The GCU transmits a diagnostic signal back to the engine ECM. If the GCU detects a fault for one of the glow plugs, a diagnostic code will become active for that glow plug.



Illustration 1g03723539
Schematic diagram for the glow plug starting aid circuit
Not all connectors are shown. Refer to the Electrical Schematic for the application.


Illustration 2g03724059
View of the pin locations on the P1 connector for the Glow Plug Control unit (GCU)
(22) GCU diagnostic return
(26) GCU control signal
(41) GCU ground


Illustration 3g02674096
View of the pin locations on the GCU
(1) Glow plug cylinder 3
(2) Glow plug cylinder 1
(3) GCU diagnostic return
(4) Battery +
(5) GCU ground
(6) Glow plug cylinder 4
(7) Glow plug cylinder 2
(8) Glow plug control

Glow Plug Starting Aid Override

Activate this override using the electronic service tool. This override is used to check that the glow plugs are functioning correctly. The override will remain active until switched off using the electronic service tool.

Navigate to the following menu options in the electronic service tool in order to access the "Glow Plug Starting Aid Override":

  • Diagnostics

  • Diagnostic Tests

  • Override Parameters

Table 2
Troubleshooting Test Steps  Values  Results 

1. Inspect Electrical Connectors and Wiring

A. Check the fuses.

B. Inspect the terminals on the GCU. Refer to Troubleshooting, "Electrical Connector - Inspect" for details.

C. Inspect the connectors between the GCU and the glow plugs.

D. Inspect the terminals on the P1/J1 ECM connector and all other connectors associated with the glow plug circuit.

E. Perform a 30 N (6.7 lb) pull test on each of the wires in the ECM connector that are associated with glow plug circuit.

F. Check the harness for abrasion and for pinch points from the glow plugs to the GCU, and from the GCU to the ECM.
 

Damaged wire or connector 

Result: A damaged wire or damaged connector was found. A fuse is blown.

Repair: Repair the damaged wire or the damaged connector. Replace any blown fuses
Use the electronic service tool to clear all logged diagnostic codes. Verify that the repair eliminates the fault.

Result: All connectors, pins, and sockets are correctly connected and/or inserted and the harness is free of corrosion, of abrasion or of pinch points.

Proceed to Test Step 2.
 

2. Check for Active Diagnostic Codes or Logged Diagnostic Codes

A. Connect the electronic service tool to the diagnostic connector.

B. Turn the keyswitch to the ON position. Do not start the engine.

C. Use the electronic service tool to override the glow plug start aid.

D. Check for active diagnostic codes or recently logged diagnostic codes.

E. Use the electronic service tool to turn off the glow plug start aid.

F. Turn the keyswitch to the OFF position.
 

Diagnostic codes 

Result: A 5324-7, 5325-7, 5326-7, or 5327-7 diagnostic code is active or recently logged.

Proceed to Test Step 3.

Result: A 676-XX diagnostic code is active or recently logged

Proceed to Test Step 6.

Result: An active diagnostic code or a recently logged diagnostic code was not displayed.

Repair: In order to identify intermittent faults, refer to Troubleshooting, "Electrical Connector - Inspect".
 

3. Check the Glow Plug for the Suspect Cylinder

A. Turn the keyswitch to the OFF position.

B. Disconnect the connectors for the glow plugs in any suspect cylinders. Refer to Table 1 in order to identify which cylinders are suspect.

C. Use a multimeter to measure the resistance between the suspect glow plug connector and a suitable engine ground.
 

Resistance 

Result: The measurement indicates an open circuit between the glow plug and the ground point.
The glow plug is faulty.

Repair: Replace the suspect glow plug. Refer to Disassembly and Assembly, "Glow Plugs - Remove and Install".

Use the electronic service tool to override the glow plug start aid and verify that the repair eliminates the fault. Clear all logged diagnostic codes.

Result: The measurement indicates that there is a resistance between the glow plug and the ground point.

The glow plug is OK.
Proceed to Test Step 4.
 

4. Check the Glow Plug Wiring for an Open Circuit

A. Turn the keyswitch to the OFF position.

B. Disconnect the connectors for any suspect glow plugs. Disconnect the connector for the GCU.

C. Use a multimeter to measure the resistance between the harness connector for the suspect glow plug and the appropriate terminal on the GCU connector.
 

Less than 5 Ohms 

Result: At least one of the resistance measurements is greater than 5 Ohms.
The fault is in the wiring between the suspect glow plug and the GCU.

Repair: Check all wiring between the suspect glow plug and the GCU. Refer to the Electrical Schematic for the application.
Make any necessary repairs.

Result: All resistance measurements are less than 5 Ohms.

Reconnect all connectors. Proceed to Test Step 5.
 

5. Check the Glow Plug Wiring for a Short Circuit

A. Turn the keyswitch to the OFF position.

B. Disconnect the connector for the suspect glow plug.

C. Use a multimeter to measure the resistance between the harness connector for the suspect glow plug and engine ground.
 

Greater than 1 k Ohm 

Result: The measured resistance is less than 1 k Ohm.
There is a short to ground in the wiring for the suspect glow plug.

Repair: Check the wiring between the suspect glow plug and the GCU. Refer to the Electrical Schematic for the application.
Make any necessary repairs.

Result: The measured resistance is greater than 1 k Ohm.
The wiring is OK.

Repair: Install a replacement GCU.
Use the electronic service tool to override the glow plug start aid and verify that the repair eliminates the fault.
 

6. Check that the GCU is Receiving the Correct Voltage

A. Turn the keyswitch to the OFF position.

B. Disconnect the GCU.

C. Turn the keyswitch to the ONposition.

D. Measure the voltage between pin 4 on the harness connector for the GCU and a suitable ground.
 

10 V to 14 V 

Result: The measured voltage is not within the expected range.

Repair: Check the fuse for the GCU. If the fuse is blown, replace the fuse.
If the fuse is replaced and the fault reoccurs, there is a short in the wiring between the battery supply and pin 4 on the GCU.
If the fuse is not blown, there is an open circuit in the wiring between the battery supply and pin 4 on the GCU.
Repair the faulty wiring or replace the faulty wiring. Reconnect the GCU. Use the electronic service tool to override the glow plug start aid and verify that the repair eliminates the fault.
Clear all logged diagnostic codes.

Result: The measured voltage is within the expected range.

Proceed to Test Step 7.
 

7. Check That the GCU is Grounded Correctly

A. Turn the keyswitch to the OFF position.

B. Disconnect the GCU.

C. Turn the keyswitch to the ON position.

D. Measure the voltage between pin 4 and pin 5 on the harness connector for the GCU. 

10 V to 14 V 

Result: The measured voltage is not within the expected range.
The fault is in the wiring between pin 5 on the harness connector for the GCU and P1:41.

Repair: Inspect the 9-pin engine interface connector. Repair the faulty wiring or replace the faulty wiring. Use the electronic service tool to override the glow plug start aid and verify that the repair eliminates the fault.
Clear all logged diagnostic codes.

Result: The measured voltage is within the expected range.

Proceed to Test Step 8.
 

8. Check the Type of Active Diagnostic Code

A. Turn the keyswitch to the ON position.

B. Use the electronic service tool to override the glow plug starting aid.

C. Check for active diagnostic codes.

D. Use the electronic service tool to turn off the glow plug starting aid.

E. Turn the keyswitch to the OFF position.
 

Diagnostic Codes
 

Result: A 676-5 diagnostic code is active

Proceed to Test Step 9.

Result: A 676-6 diagnostic code is active

Proceed to Test Step 11.

Result: A 676-19 diagnostic code is active

Proceed to Test Step 13.
 

9. Create a Short Circuit at the Harness Connector for the GCU

A. Turn the keyswitch to the OFF position.

B. Disconnect the GCU.

C. Fabricate a jumper wire that is 15 cm (6 inch) long.

D. Install the jumper wire between pin 5 and pin 8 on the harness connector for the GCU.

E. Turn the keyswitch to the ON position.

F. Use the electronic service tool to override the glow plug starting aid.

G. Check for active diagnostic codes.

H. Use the electronic service tool to turn off the glow plug starting aid.

I. Turn the keyswitch to the OFF position.

J. Remove the jumper wire.
 

Diagnostic codes
 

Result: A 676-6 diagnostic code is active with the jumper installed.

Repair: Install a replacement GCU.
Use the electronic service tool to override the glow plug starting aid and verify that the repair eliminates the fault.
Clear all logged diagnostic codes.

Result: A 676-5 diagnostic code is active with the jumper installed.

Proceed to Test Step 10. 

10. Check the Resistance Between the GCU and the ECM

A. Turn the keyswitch to the OFF position.

B. Disconnect the GCU. Disconnect the P1/J1 connector.

C. Measure the resistance between pin 8 on the harness connector for the GCU and P1:26.
 

Less than 5 Ohms
 

Result: The measured resistance is not within the expected range.
There is an open circuit or high resistance in the wiring between pin 8 on the harness connector for the GCU and P1:26.

Repair: Inspect the 9-pin engine interface connector. Repair the faulty wiring or replace the faulty wiring.

Result: The measured resistance is within the expected range.

Contact the Dealer Solution Network (DSN).
 

11. Create an Open Circuit at the GCU Harness Connector

A. Turn the keyswitch to the OFF position.

B. Disconnect the GCU.

C. Turn the keyswitch to the ON position.

D. Use the electronic service tool to override the glow plug start aid.

E. Check for active diagnostic codes.

F. Use the electronic service tool to turn off the glow plug start aid.

G. Turn the keyswitch to the OFF position.
 

Diagnostic codes
 

Result: A 676-5 diagnostic code is active with the GCU disconnected.

Repair: Install a replacement GCU.
Use the electronic service tool to override the glow plug starting aid and verify that the repair eliminates the fault.
Clear all logged diagnostic codes.

Result: A 676-6 diagnostic code is active with the GCU disconnected.

Proceed to Test Step 12.
 

12. Check the GCU control Wire for a Short Circuit

A. Turn the keyswitch to the OFF position.

B. Disconnect the P1/J1 connector. Disconnect the GCU.

C. Use a multimeter to measure the resistance between P1:26 and all other terminals on the P1 connector.
 

Greater than 1 k Ohm
 

Result: At least one of the resistance measurements is not within the expected range.
There is a short circuit in the wiring between the GCU connector and the P1 ECM connector.

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 within the expected range.

Contact the Dealer Solution Network (DSN).
 

13. Check the Diagnostic Return Wire From the GCU

A. Turn the keyswitch to the OFF position.

B. Disconnect the GCU. Disconnect the P1/J1 connector.

C. Measure the resistance between pin 3 on the harness connector for the GCU and P1:22.
 

Less than 5 Ohms 

Result: The measured resistance is greater than 5 Ohms.
There is an open circuit or high resistance in the wiring.

Repair: Repair the faulty wiring or replace the faulty wiring.

Result: The measured resistance is less than 5 Ohms.

Contact the Dealer Solution Network (DSN).
 

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