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P codepowertrainMedium severity

P0673Cylinder 3 Glow Plug Circuit

A fault has been detected in the cylinder 3 glow plug circuit on a diesel engine, leaving that cylinder without proper cold-start heating.

Definition

During cold starts the glow plug control module powers each glow plug and verifies circuit integrity by monitoring current flow; P0673 sets when the cylinder 3 circuit shows an open, short, or implausible current. The engine will still start in mild weather, but cold-weather symptoms include extended cranking, a distinct cold miss on cylinder 3, shaking at idle until warm, and white smoke. The MIL or glow plug lamp comes on, and a current code fails an OBD emissions inspection; systems that use post-start or regeneration glow phases lose those functions on the affected cylinder as well.

Common causes

  • Open cylinder 3 glow plug element from normal end-of-life failure
  • Loose, corroded, or oil-contaminated terminal at the plug
  • Wiring damage between the glow plug control module and cylinder 3
  • Excessive carbon deposits on the plug tip
  • Faulty glow plug control module output stage

Common misdiagnoses

  • Replacing the glow plug control module when only the plug is open
  • Swapping batteries or glow plug relays on systems that don't use a single relay
  • Replacing the cylinder 3 injector for a cold-only miss
  • Performing compression testing first for what is an electrical circuit code

Troubleshooting steps

  1. 1.Measure the cylinder 3 plug's resistance

    With the feed disconnected, terminal-to-ground should read about 0.5-2 ohms depending on plug type; OL confirms an open element.

  2. 2.Compare all cylinders' readings

    Test the full set while you're there — plugs measurably drifting from the others are candidates for preventive replacement.

  3. 3.Inspect the cylinder 3 lead and terminal

    Verify terminal tightness, look for corrosion or oil intrusion, and check the harness where it routes across the head for chafing.

  4. 4.Verify output during a commanded glow cycle

    Activate the glow plugs with a scan tool or cold start and confirm the specified voltage arrives at the cylinder 3 terminal.

  5. 5.Replace the plug with correct technique

    Remove carefully on engines known for seized plugs (penetrating soak, warm engine, incremental back-and-forth) and torque the replacement to specification, typically 8-15 Nm.

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