P2306: Ignition Coil C Primary Control Circuit Low
Do not keep driving
Stop if the engine light is flashing. Ask for the spark plug well to be checked for oil or water before a coil is fitted. A leaking valve cover gasket fills the well with oil, which ruins coils one after another — so if this cylinder has already had a coil, the well is the thing to fix rather than the coil. Mention it if the misfire started after heavy rain or a car wash.
What this code means
Coil C's primary control circuit reads below its valid range, normally a short to ground.
One cause is specific to how modern coils are mounted and is worth checking before anything electrical: what is in the spark plug well. Coil-on-plug designs drop the coil down a deep tube in the cylinder head, and that tube collects whatever leaks into it.
- Oil, from a leaking valve cover gasket or plug well seal. It soaks the coil boot, degrades the rubber, and provides a path for the spark to track to earth rather than jump the gap.
- Water, from a blocked scuttle drain or a washer leak, which is why some of these faults appear only after rain or a car wash.
Both destroy coils repeatedly rather than once. A coil replaced without curing what is filling the well fails again, usually within months, and that pattern — one cylinder that keeps eating coils — is this and almost nothing else.
Likely causes
Start here
- Oil in the spark plug well · moderate
- Water in the spark plug well · easy
- Faulty ignition coil · easy
Less common
- Wiring shorted to ground · moderate
- Perished or tracking coil boot · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P2306.