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P codepowertrainMedium severity

P06C0Cylinder 8 Glow Plug Circuit Range/Performance

The glow plug control module has detected that the cylinder 8 glow plug circuit is drawing current outside its expected range, indicating a degraded plug or circuit on a diesel engine.

Definition

The glow plug control module monitors current and effective resistance in each glow plug circuit during pre-heat and post-heat phases. P06C0 sets when the cylinder 8 circuit is not open or shorted but its measured current falls outside the calibrated range, most often from an aging plug element or added resistance at a terminal. Expect hard cold starts, white smoke and rough running when cold, and a glow plug lamp or MIL that can fail an emissions inspection; warm-weather driveability is often unaffected.

Common causes

  • Aged or degraded cylinder 8 glow plug with out-of-spec resistance
  • Corroded or loose glow plug terminal or supply harness connection
  • High-resistance wiring between the control module and the plug
  • Wrong glow plug type or rating installed in cylinder 8
  • Failing glow plug control module channel
  • Degraded module power feed or ground raising circuit voltage drop

Common misdiagnoses

  • Replacing the full glow plug set when only cylinder 8 is at fault
  • Replacing the glow plug control module instead of repairing a corroded connection
  • Charging-system repairs for what is a single-circuit fault
  • Injector replacement for cold-start smoke caused by the weak plug

Troubleshooting steps

  1. 1.Scan and record data

    Read codes from the glow plug module and PCM and note whether adjacent cylinders show similar range/performance codes, which points to shared wiring or the module.

  2. 2.Measure plug resistance

    Measure the cylinder 8 plug from terminal to ground; readings are normally well under 2 ohms, and any significant deviation from sibling cylinders is suspect.

  3. 3.Inspect connections

    Look for corrosion, overheated terminals, or loose nuts at the plug and chafed insulation along the valley or bank harness.

  4. 4.Compare live current

    Amp-clamp the cylinder 8 feed during pre-heat and compare inrush and settled current with a known-good cylinder.

  5. 5.Confirm correct part number

    Verify the installed plug matches OE specification, since an incorrect-rating plug will keep the circuit out of range.

  6. 6.Repair, clear, retest

    Replace the plug or repair wiring, torque the new plug to spec (typically 10-15 Nm), then verify no reset over multiple cold-start pre-heat cycles.

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