Powertrain, generic · Computer and auxiliary outputs

P06B9 Cylinder 1 Glow Plug Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The glow module calculates each plug's resistance from voltage and current while glowing. 'Range/performance' means the circuit is electrically intact but the resistance or current lies outside the specified window – typically an aged, high-resistance or wrong plug or contact resistance at the connector. CARB requires a single plug outside specification to be detected from model year 2010. Ford's 2023 6.7 L/3.0 L Power Stroke runs this check during heating after the open and short checks and flags a circuit above 2 Ω after about 3 s. GM does not use this code family. Ram's 6.7 L Cummins (from model year 2025, with glow plugs instead of the grid heater) set these codes falsely; the fix was reprogramming the engine module. On the 2014–15 Ram ProMaster 3.0 L diesel, plugs without an inner O-ring caused it; all plugs were replaced. P06B9 concerns the glow plug of cylinder 1 alone; the same plug's open circuit is P0671, its control circuit low and high P066A/P066B, and an incorrect plug fitted P06C5.

Likely causes

Glow plug cylinder 1 aged or high-resistance
Contact resistance at plug connector or terminal nut
Wrong plug type or a plug with a manufacturing fault
Engine or glow module software (Ram 6.7 L from 2025)

Symptoms

  • Check engine and glow plug lamp
  • Harder cold start in frost
  • Rough running and white smoke after a cold start
  • Often no symptom when warm

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

glow plugglow plug wiringglow plug control module

Related codes

P0671P066AP066BP06C5P0670P052F

References: law.cornell.edu, fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov.