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P06BC

Cylinder 4 Glow Plug Circuit Range/Performance.

  • Generic
  • Powertrain
  • Generic code
  • Low severity

How this code is built

P
SystemPowertrain
0
Defined bySAE, the same on every car
6
AreaComputer and output circuits
BC
FaultThe specific fault in that area

What it means

P06BC is the generic SAE J2012 code for a range or performance fault in the cylinder 4 glow plug circuit. The control unit monitors the glow plug circuit, either through a driver stage or a separate glow plug control module, and has seen current, voltage or resistance for cylinder 4 outside the expected range. The circuit is not necessarily open or shorted, but it is not behaving as the control unit expects.

Symptoms

  • Engine warning light or glow plug warning light on
  • Hard starting or extended cranking when the engine is cold
  • White smoke and rough running for the first minutes after a cold start
  • Misfire or uneven idle on cylinder 4 until the engine warms up
  • Slightly higher fuel consumption or noisier running when cold
  • No noticeable symptoms when the engine is warm

Possible causes

  • Cylinder 4 glow plug degraded, with resistance or current draw out of rangelikely
  • Corroded, loose or damaged connector or terminal at the cylinder 4 glow pluglikely
  • Wiring fault to the cylinder 4 glow plug, such as chafed insulation, high resistance or a poor earthpossible
  • Poor power supply to the glow plug system, such as a weak battery, a corroded supply connection or a failing relay or fusepossible
  • Fault in the glow plug control module or driver stage for cylinder 4possible
  • Outdated or faulty control unit software where the manufacturer has issued a correction (model dependent)rare

How to diagnose

  1. Read all stored and pending codes with freeze frame data, and note any other glow plug codes for other cylinders or the control module
  2. Check battery condition and charging voltage, as low voltage can upset glow plug circuit monitoring
  3. Inspect the cylinder 4 glow plug connector, terminal and wiring for corrosion, heat damage, chafing or looseness
  4. Check the glow plug supply fuse, relay and power feed connections as per the model's wiring diagram
  5. Measure the cylinder 4 glow plug resistance cold and compare it with the specification for that engine, with the plug disconnected
  6. Compare the current draw or live data for each glow plug, if the system supports it, to spot cylinder 4 deviating from the others
  7. Check voltage supply and earth at the plug connector during a glow cycle, and test the wiring for continuity and resistance
  8. Check for applicable software updates or technical bulletins for the model and engine before replacing the control module

How to fix

  • Replace the cylinder 4 glow plug if its resistance or current draw is out of specification, taking care when removing it to avoid breakage in the head
  • Clean or repair the connector and terminal, or replace them if corroded or heat damaged
  • Repair or replace damaged wiring or earth connections on the cylinder 4 circuit
  • Restore the power supply by replacing a faulty fuse or relay, or by repairing poor connections, and replace a weak battery
  • Replace the glow plug control module if the checks show the driver stage is faulty
  • Apply a manufacturer software update where one is known to correct this fault

Can I keep driving?

Low severity

The car can normally be driven, but cold starting may be poor and smoke or roughness may occur until warm. Book it in soon, especially before cold weather, and avoid repeated cold starts if it runs badly.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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