What it means
The primary control circuit of ignition coil F reads a voltage below the expected level — usually a short to ground on the primary driver wire or a low-resistance fault in the coil primary winding. Coil F cannot build a normal charge, so the cylinder it fires misfires, especially under load. Causes: short to ground in the primary wiring, an internal coil primary fault, or a faulty ECU/igniter driver.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Coil F's primary control circuit carries the low-voltage current used to build the magnetic field that produces a spark. The control module sets this code when it detects voltage below the expected level, such as from a short to ground or a coil primary fault, and the cylinder served by coil F may misfire.
Common causes
Most likely first.
- Primary winding shorted to ground or harness chafed
- Coil F internal driver fault
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light on, possibly flashing
- Engine misfire or rough idle
- Hesitation under acceleration
- Reduced power
How to diagnose it
- Record freeze-frame data and check live misfire counts to confirm whether the coil F cylinder is affected.
- With the ignition off, inspect coil F's connector and harness for chafing, pin damage, corrosion, or wiring touching ground.
- Check the coil F connector seating and inspect its terminals for corrosion or poor contact.
- Use the wiring diagram to test the coil F primary control circuit for a short to ground and compare results with the manufacturer's specification.
- If the harness checks out, test coil F's primary winding and driver circuit using the manufacturer's procedure.
Common fixes
- Clean and secure corroded or loose coil F connector terminals.
- Repair chafed coil F wiring that is shorted to ground.
- Replace coil F if its primary winding fails testing.
- Repair the control driver only if circuit tests identify it as faulty.
Can I keep driving?
Limit driving and avoid heavy acceleration because the coil F cylinder may misfire under load. If the check-engine light flashes or the engine runs very roughly, stop when safe to reduce the risk of catalytic-converter damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.