P06BA: Cylinder 2 Glow Plug Circuit Range/Performance
What to do
Ask for all the glow plugs to be tested, not just this one. This kind of fault catches a plug that is drifting rather than one that has failed, and they age as a set — so the others are usually close behind, and the labour is the same whether one comes out or all of them.
Ask for the connector and supply strap to be checked first, since corrosion adds resistance the module reads as a failing plug.
Mention whether the plugs have been replaced before and whether they were original parts, since a plug of the wrong specification sets this while being new.
Expect hard starting and white smoke on cold mornings, getting worse as the weather cools.
What this code means
Cylinder 2's glow plug circuit is electrically valid but not behaving correctly.
The module measures each plug's resistance to infer its temperature, and this one is not matching what a healthy plug would give.
Unlike the control circuit codes, this family runs consecutively — P06B9 through P06BE for cylinders 1 to 6 — which makes it the more predictable of the two glow plug sets. That is worth noting precisely because its sibling family does not, and mixing the two conventions up is how the wrong cylinder gets diagnosed.
The practical value of range/performance codes is that they catch a plug before it fails outright. A plug that has gone open or short is obvious; a plug drifting out of specification still works, badly, and this code is the early warning.
Which makes a single range/performance code a good moment to test the whole set rather than replace one plug. They age together, so one drifting usually means the others are close behind — and the labour and the snapping risk are the same whether one comes out or four do.
Check the supply connection first as always. Added resistance in the strap or connector is indistinguishable, from the module's point of view, from the plug itself changing.
Likely causes
Start here
- Failed glow plug · moderate
- High resistance in sensor wiring · moderate
- Corroded or loose connector · easy
Less common
- Incorrect glow plugs fitted · moderate
- Broken glow plug supply wire · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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