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P codepowertrainMedium severity

P06C8Cylinder 4 Glow Plug Incorrect

The glow plug control module has determined that the glow plug installed in cylinder 4 does not match the expected type, based on its electrical signature.

Definition

The glow plug control module validates each plug's cold resistance and heating-current profile against the characteristics of the plug specified in its calibration. P06C8 sets when the cylinder 4 plug's measured signature corresponds to a different plug type or voltage rating, most often after an incorrect replacement part was installed. The module may reduce or cut drive to protect the element, producing hard cold starts, cold-start smoke, and a glow plug lamp or MIL; an overdriven wrong plug risks overheating and tip loss into the cylinder.

Common causes

  • Incorrect voltage-rating or wrong-type plug installed in cylinder 4
  • Non-matching aftermarket plug substituted for the OE part
  • Severely degraded plug presenting an incorrect signature
  • Corroded terminal or harness resistance skewing the measurement
  • Wrong-variant or miscoded glow plug control module

Common misdiagnoses

  • Replacing the glow plug control module rather than the mismatched plug
  • Wiring repairs when the plug's rating is simply wrong
  • Replacing the whole plug set when only cylinder 4 is affected
  • Charging-system diagnosis for a plug-signature fault

Troubleshooting steps

  1. 1.Verify the installed plug

    Compare the cylinder 4 plug part number with the OE catalog, confirming correct voltage rating for this glow system.

  2. 2.Measure cold resistance

    Check plug-to-ground resistance against specification and against the other cylinders for an obvious mismatch.

  3. 3.Inspect the circuit path

    Look for corrosion, loose terminal hardware, or harness damage that could distort the current measurement.

  4. 4.Compare heating current

    Amp-clamp during pre-heat and compare cylinder 4's inrush and settle behavior with a known-good cylinder.

  5. 5.Fit the correct part

    Install the OE-specified plug torqued to spec (typically 10-15 Nm) after cleaning the plug bore.

  6. 6.Clear and confirm

    Clear the code and run multiple pre-heat cycles to verify the detection does not repeat.

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