Ignition Coil F Primary/Secondary Circuit
What it means
The engine computer has detected an electrical fault in the circuit of ignition coil F. It appears on engines with six or more cylinders, where coil F usually serves cylinder 6, which should be confirmed in the service manual, and a misfire in that cylinder normally comes with it.
Symptoms4
- Check engine light on, possibly flashing during misfires.
- Noticeable shaking at idle and stumbling on acceleration.
- A misfire code for the cylinder served by coil F, often P0306.
- Higher fuel consumption.
Possible causes6
- Failed ignition coil F.
- Loose or corroded coil F connector.
- Open or shorted coil F control wire.
- Fault in the shared coil supply or ground.
- Damaged spark plug or a cracked coil boot leaking spark.
- Failed driver circuit inside the engine computer (rare).
How to diagnose5
- Identify the cylinder coil F serves from the service manual.
- Inspect the connector, wiring and coil boot for damage or burn marks.
- Swap coil F with another coil on the same bank and clear the codes to see whether the fault follows it.
- Measure supply and ground and check control pulses at the coil connector.
- Inspect that cylinder's plug, and trace the control wire back to the computer if the fault stays in place.
How to fix5
- Clean the connector and repair its terminals.
- Repair the damaged control or supply wire.
- Replace ignition coil F if the fault follows it.
- Replace the damaged plug in the same cylinder.
- Clear the codes, road test and confirm the code does not return.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
The cost stays low for a connector or wire fix and rises with a new coil and plug; labor increases when the coil is on a hard-to-reach rear bank.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026
Frequently asked questions
Is swapping the coil with another cylinder safe?
Yes, if the coils are identical. It is the quickest way to confirm coil F is bad before buying one, as long as you clear the codes and test drive after the swap.
What happens if I ignore the code?
Cylinder 6 is likely not firing well, so unburned fuel enters the catalytic converter, overheats it and can destroy it, on top of the shaking and power loss.
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What was wrong? (optional)
This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.
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