P0679: Glow Plug Control Module Circuit Low

Definition

The OBD2 code P0679 indicates a low voltage or malfunction in the glow plug control module circuit, which affects the operation of the glow plugs in a diesel engine

Common causes

Faulty glow plug control module
Damaged wiring or connectors in the glow plug circuit
Short circuit in the glow plug circuit
Open circuit in the glow plug circuit
Faulty glow plugs
Poor ground connection
Blown fuse related to the glow plug system
Corrosion or damage at electrical connections

Common misdiagnoses

Faulty glow plugs
Bad glow plug relay
Wiring issues or shorts
Faulty engine control module (ECM)
Battery or charging system problems
Fuel system issues
Injector problems
Compression issues
Incorrectly diagnosed as a fuel injection timing issue
Misinterpretation of other related codes

Troubleshooting steps

1. Check the Code

Use an OBD-II scanner to confirm that P0679 is the only code present. If there are other codes, they may provide additional context for the issue
2. Inspect the Glow Plug Control Module
3. Visually inspect the glow plug control module for any signs of damage, corrosion, or loose connections
4. Ensure that the module is securely mounted and that all connectors are clean and free of debris
5. Test the Glow Plugs
6. Check the resistance of each glow plug using a multimeter. The resistance should typically be within the manufacturer's specified range (usually a few ohms)
7. If any glow plugs are open or shorted, they should be replaced
8. Check Wiring and Connectors
9. Inspect the wiring harness and connectors leading to the glow plug control module and glow plugs for any signs of wear, fraying, or damage
10. Look for any loose or corroded connections that could cause a poor electrical signal
11. Test the Glow Plug Control Module
12. If the wiring and glow plugs are in good condition, test the glow plug control module itself. This may require specific diagnostic tools or procedures as outlined in the vehicle's service manual
13. Check for proper voltage and ground at the module's connectors
14. Check Fuses and Relays
15. Inspect any fuses or relays associated with the glow plug system. Replace any blown fuses and test relays for proper operation
16. Check for Short Circuits
17. Use a multimeter to check for short circuits in the wiring. A short to ground can cause the circuit to read low voltage
18. Clear the Codes and Test Drive
19. After performing repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns
20. Consult the Service Manual
21. If the issue persists, consult the vehicle's service manual for specific diagnostic procedures and specifications related to the glow plug control system
22. Seek Professional Help
23. If you are unable to resolve the issue after these steps, it may be best to consult a professional mechanic or technician who has experience with diesel engines and glow plug systems. By following these steps, you should be able to identify and resolve the issue related to the P0679 code

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Check the Code

2. Inspect the Glow Plug Control Module

3. Visually inspect the glow plug control module for any signs of damage, corrosion, or loose connections

4. Ensure that the module is securely mounted and that all connectors are clean and free of debris

5. Test the Glow Plugs

6. Check the resistance of each glow plug using a multimeter. The resistance should typically be within the manufacturer's specified range (usually a few ohms)

7. If any glow plugs are open or shorted, they should be replaced

8. Check Wiring and Connectors

9. Inspect the wiring harness and connectors leading to the glow plug control module and glow plugs for any signs of wear, fraying, or damage

10. Look for any loose or corroded connections that could cause a poor electrical signal

11. Test the Glow Plug Control Module

12. If the wiring and glow plugs are in good condition, test the glow plug control module itself. This may require specific diagnostic tools or procedures as outlined in the vehicle's service manual

13. Check for proper voltage and ground at the module's connectors

14. Check Fuses and Relays

15. Inspect any fuses or relays associated with the glow plug system. Replace any blown fuses and test relays for proper operation

16. Check for Short Circuits

17. Use a multimeter to check for short circuits in the wiring. A short to ground can cause the circuit to read low voltage

18. Clear the Codes and Test Drive

19. After performing repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

20. Consult the Service Manual

21. If the issue persists, consult the vehicle's service manual for specific diagnostic procedures and specifications related to the glow plug control system

22. Seek Professional Help

23. If you are unable to resolve the issue after these steps, it may be best to consult a professional mechanic or technician who has experience with diesel engines and glow plug systems. By following these steps, you should be able to identify and resolve the issue related to the P0679 code