Cylinder 1 Glow Plug Circuit
P0671 indicates the glow plug circuit for cylinder #1 is not functioning properly. Glow plugs are heating elements in diesel engines that warm the combustion chamber to aid cold starting. A failure in this circuit prevents proper preheating and can cause starting difficulty, especially in cold conditions.
What You Might Notice
- Check engine light illuminated
- Hard starting in cold weather
- Rough idle when first starting
- White smoke on cold startup
- Engine may start but with difficulty
Most Common Causes
- 1
Failed Glow Plug
The glow plug element for cylinder #1 has burned out or failed electrically. This is the most common cause and requires replacement of the glow plug.
- 2
Faulty Glow Plug Relay
The relay controlling the glow plug circuit is stuck open or has poor contact. This prevents voltage from reaching the glow plug even if the plug itself is functional.
- 3
Wiring or Connector Issues
Corroded connectors, loose terminals, or damaged wiring in the glow plug circuit can interrupt power delivery to cylinder #1's glow plug.
- 4
Engine Control Module Defect
A faulty ECM may fail to properly control the glow plug circuit or incorrectly detect glow plug operation, though this is less common than hardware failures.
How to Diagnose It
- 1
Check Failed Glow Plug — The glow plug element for cylinder #1 has burned out or failed electrically. This is the most common cause and requires replacement of the glow plug.
- 2
Check Faulty Glow Plug Relay — The relay controlling the glow plug circuit is stuck open or has poor contact. This prevents voltage from reaching the glow plug even if the plug itself is functional.
- 3
Check Wiring or Connector Issues — Corroded connectors, loose terminals, or damaged wiring in the glow plug circuit can interrupt power delivery to cylinder #1's glow plug.
- 4
Check Engine Control Module Defect — A faulty ECM may fail to properly control the glow plug circuit or incorrectly detect glow plug operation, though this is less common than hardware failures.
How to Fix It
- 1
Replace Glow Plug #1
Remove the faulty glow plug from cylinder #1 using appropriate socket and tools. Install a new OEM or equivalent glow plug rated for your diesel engine model. Clear the code after replacement and test cold start operation.
- 2
Inspect and Clean Connectors
Locate the glow plug circuit connectors and wiring. Clean any corrosion from terminals using contact cleaner and a wire brush. Reseat all connectors firmly to ensure good electrical contact.
- 3
Test and Replace Glow Plug Relay
Using a multimeter, test the glow plug relay for continuity and proper switching. If faulty, replace the relay with an OEM part. This typically resolves issues affecting the entire glow plug circuit.
- 4
Repair Wiring Damage
Inspect the full glow plug circuit wiring for breaks, fraying, or damaged insulation. Repair or replace damaged sections using appropriate automotive wire and connectors. Ensure proper routing away from engine heat sources.
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