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P codepowertrainMedium severity

P06BBCylinder 3 Glow Plug Circuit Range/Performance

The glow plug circuit for cylinder 3 is drawing current outside the expected range, usually because that glow plug is degraded or its circuit has excess resistance.

Definition

On diesel engines, the glow plug control module measures the current through each individual glow plug during pre-glow and after-glow phases. P06BB sets when cylinder 3's circuit current or calculated resistance falls outside the expected window — a plug that is open, worn, or the wrong type, or a circuit with corroded connections. Symptoms are hard starting in cold weather, cold-engine misfire or rough idle, white smoke on startup, and an illuminated glow plug lamp or MIL; in warm conditions there may be no symptom at all, but the MIL can still cause an emissions-inspection failure.

Common causes

  • Failed or worn cylinder 3 glow plug (most common)
  • Corroded or loose terminal at the glow plug or its connector
  • Damaged wiring between the glow plug control module and the plug
  • Wrong glow plug part number with incorrect resistance rating
  • Glow plug control module output channel fault

Common misdiagnoses

  • Glow plug control module replaced when a single plug is out of spec
  • Battery or starter replaced for the hard cold-start complaint
  • Injectors blamed for cold white smoke that traces to the dead glow plug

Troubleshooting steps

  1. 1.Measure cylinder 3 glow plug resistance

    Disconnect and measure plug-to-ground resistance — most modern plugs read roughly 0.5–2 ohms; compare directly against the other cylinders and treat an outlier or open reading as the fault.

  2. 2.Check circuit current during pre-glow

    Clamp an ammeter on the cylinder 3 feed during an active glow cycle and compare amperage to a known-good cylinder — low or zero current confirms the circuit fault.

  3. 3.Inspect the connector and wiring

    Look for heat-hardened insulation, corroded terminals, and chafed wiring between the module and the plug, which add resistance the module reads as out-of-range.

  4. 4.Verify the correct plug part number

    Confirm the installed plug matches the specified voltage/resistance rating — a wrong plug reads permanently out of range to the module.

  5. 5.Replace the glow plug and retest

    After replacement, run a glow cycle and confirm the current matches the sibling cylinders and the code does not return.

  6. 6.Test the module output last

    If the plug and wiring test good, swap the cylinder 3 output to another channel (where the design allows) or scope the output to confirm a module fault before replacing it.

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