Glow Plug Module Control Circuit
P0670 indicates a circuit fault in the glow plug control module, which manages the heating elements that warm the combustion chamber for diesel engine cold starts. Without proper glow plug function, the engine may have difficulty starting, especially in cold conditions, and could produce white smoke on startup.
What You Might Notice
- Hard starting, especially in cold weather
- White or gray smoke on startup
- Rough idle after cold start
- Reduced engine power during warm-up
- Check Engine Light illuminated
Most Common Causes
- 1
Faulty Glow Plug Control Module
The control module that manages glow plug operation has failed electrically or internally. This is the most common cause of P0670 codes.
- 2
Defective Glow Plugs
One or more glow plugs have failed open or short, preventing proper combustion chamber preheating and causing the module to detect an abnormal circuit condition.
- 3
Corroded or Loose Wiring Connections
Poor electrical connections between the glow plug control module and glow plugs, or at battery connections, create high resistance and circuit faults.
- 4
Engine Control Module (ECM) Failure
A defective ECM that communicates with the glow plug control module may send incorrect signals or fail to properly control the glow plug system.
How to Diagnose It
- 1
Check Faulty Glow Plug Control Module — The control module that manages glow plug operation has failed electrically or internally. This is the most common cause of P0670 codes.
- 2
Check Defective Glow Plugs — One or more glow plugs have failed open or short, preventing proper combustion chamber preheating and causing the module to detect an abnormal circuit condition.
- 3
Check Corroded or Loose Wiring Connections — Poor electrical connections between the glow plug control module and glow plugs, or at battery connections, create high resistance and circuit faults.
- 4
Check Engine Control Module (ECM) Failure — A defective ECM that communicates with the glow plug control module may send incorrect signals or fail to properly control the glow plug system.
How to Fix It
- 1
Test and Replace Glow Plugs
Use a multimeter to test each glow plug for continuity and resistance. Replace any failed glow plugs with OEM or equivalent diesel-rated units.
- 2
Inspect and Clean Electrical Connections
Visually inspect all wiring harnesses, connectors, and battery terminals for corrosion, looseness, or damage. Clean corroded connections with battery terminal cleaner and retighten all fasteners.
- 3
Replace Glow Plug Control Module
If glow plugs test good but the fault persists, the control module itself has likely failed. Remove the old module and install a replacement, following manufacturer specifications.
- 4
Diagnose ECM and Reprogram if Necessary
Use diesel-specific diagnostic equipment to test ECM communication with the glow plug system. May require ECM reprogramming or replacement if the module is faulty.
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