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P codepowertrainMedium severity

P0674Cylinder 4 Glow Plug Circuit

A fault has been detected in the cylinder 4 glow plug circuit on a diesel engine, preventing normal cold-start heating for that cylinder.

Definition

The glow plug control module individually switches each glow plug and confirms proper current draw; P0674 sets when the cylinder 4 circuit is open, shorted, or out of its expected current range. One dead plug typically causes longer cranking in cold weather, a cold-start miss and shake on cylinder 4 that clears as the engine warms, and white startup smoke, while warm operation is normal. The MIL or wait-to-start lamp illuminates and the code will fail an emissions inspection; diesels that run glow plugs for combustion support or DPF regeneration lose that support on cylinder 4.

Common causes

  • Burned-out (open) cylinder 4 glow plug
  • Corroded or loose connection at the plug terminal
  • Damaged wiring from the control module to cylinder 4
  • Carbon buildup on the glow plug tip
  • Failed driver channel in the glow plug control module

Common misdiagnoses

  • Replacing the glow plug control module before checking the plug
  • Replacing batteries for hard cold starts
  • Replacing the cylinder 4 injector to chase a cold miss
  • Replacing a glow plug relay on systems with individual electronic control

Troubleshooting steps

  1. 1.Resistance-test the cylinder 4 glow plug

    Disconnect the lead and measure to ground; expect approximately 0.5-2 ohms (design-dependent), with an OL reading condemning the plug.

  2. 2.Test the remaining plugs for comparison

    Matching plugs should read nearly identical; note any others drifting high on an aged set.

  3. 3.Inspect the terminal and wiring

    Check for a loose terminal nut, connector corrosion, and harness chafe along the cylinder head or valve cover.

  4. 4.Confirm the module's output during pre-glow

    Back-probe the cylinder 4 feed during a commanded glow cycle and verify the specified voltage/PWM profile is present.

  5. 5.Repair and verify

    After replacing the plug or repairing the circuit, clear codes and run repeat pre-glow cycles to confirm the fault does not return.

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