P06BD: Cylinder 5 Glow Plug Circuit Range/Performance
What to do
Ask how difficult the plugs are to reach on this engine before deciding how many to replace. On a five or six cylinder diesel the access is often poor, and replacing one plug now and another in three months can cost nearly twice as much as doing the set today.
Ask whether several cylinders have set faults. If they have, the shared supply or earth to the glow plug module is the likely cause rather than several failed plugs — a much smaller repair.
Ask for a voltage drop test on the supply under load, not just a continuity check.
Expect hard starting and white smoke on cold mornings.
What this code means
Cylinder 5's glow plug circuit is electrically valid but not behaving correctly.
A cylinder 5 glow plug code means a five or six cylinder diesel — a larger saloon, a van, a pickup or a commercial vehicle — and on those engines the practical picture changes in one important way: access is usually worse, so the set-versus-single decision matters more.
On a transverse five or a large six, reaching the rear plugs can mean removing intake pipework or engine covers, and on some engines the work is genuinely awkward. Where that is true, replacing one plug and returning for the next is close to doubling the cost of the job.
The diagnostic content is the family's. The module reads resistance to infer temperature; a drifting plug, added resistance in the supply, or a plug of the wrong specification all produce this.
The supply chain argument applies with more force on a longer engine. Six plugs fed from one strap means more terminals in series, more places for a small resistance to hide, and a longer run for the voltage to be lost along. Measure the drop under load rather than trusting continuity.
Where several cylinders show these codes together, check the module's own supply and earth before the plugs. One bad connection there starves all of them at once, and it is the cheapest thing on the list.
Likely causes
Start here
- Failed glow plug · moderate
- High resistance in sensor wiring · moderate
- Corroded or loose connector · easy
Less common
- Poor sensor ground connection · moderate
- Incorrect glow plugs fitted · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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