P0356
PowertrainIgnition Coil"F" Primary/Secondary Circuit
The ECU watches the voltage pulse in each ignition coil's primary winding every time it fires. When the pulse for coil 'F' (cylinder 6 on most engines) doesn't look right, either too high, too low, or missing entirely, it logs P0356 because the spark on that cylinder isn't being delivered properly. For you the driver, that usually means a misfire on one cylinder, a warning light, and an engine that feels rougher than it should. On a coil-on-plug setup it's normally the individual coil itself that's packed up, but the wiring and connector are close behind.
ⓘ Information only. This page provides general educational information about fault code P0356. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0356 mean?
P0356 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Ignition Coil"F" Primary/Secondary Circuit.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light, sometimes flashing when the misfire gets bad under load
- • Rough, lumpy idle and vibration through the car when sitting at the lights
- • Noticeable flat spot or hesitation under acceleration, worst pulling away or going uphill
- • A distinct misfire that you can feel as a stumble at low revs
- • Smell of unburnt petrol from the exhaust, since fuel is going through the dead cylinder unburnt
- • Fuel economy creeping up, more obvious on shorter town trips
Possible causes
Causes commonly associated with P0356, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed ignition coil on cylinder 6. This is far and away the most common cause on coil-on-plug engines, the coil simply ages and stops producing a clean spark
- 2. Corroded or loose connector at the coil. Heat and vibration up by the cylinder head wreck these plugs over time, giving an intermittent fault
- 3. Damaged wiring in the coil circuit, often chafed against the engine or melted near hot exhaust components
- 4. Worn or fouled spark plug in cylinder 6 making the coil work harder until it throws a fault
- 5. Open circuit or short to ground in the coil driver wiring back to the ECU
- 6. Faulty coil driver inside the ECU itself. Rare, but it does happen, and it's the expensive one
- 7. Rodent damage to the harness, which catches out cars left parked outside or stood for a while
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read all the stored codes first. If you've also got P0306 sitting alongside P0356, that confirms a genuine misfire on cylinder 6 rather than just an electrical glitch
- 2. Swap the cylinder 6 coil with a coil from a known-good cylinder, clear the codes, and drive it. If the fault moves to the new cylinder, you've found your dud coil and saved yourself a load of testing
- 3. Pull the connector off the coil and check it properly for green corrosion, spread pins, or a clip that isn't latching. Wiggle-test the loom while the engine idles to catch an intermittent break
- 4. Lift out the spark plug on cylinder 6 and have a look. A cracked insulator, heavy fouling, or a worn gap can drag a coil down
- 5. Measure the coil's primary and secondary winding resistance with a multimeter and compare to the workshop figures. An out-of-spec or open winding tells you the coil's finished
- 6. If the coil, plug, and connector all check out, test continuity in the wiring back to the ECU for an open or a short to ground before you start blaming the ECU
Common questions about P0356
What's this likely to cost me to sort out? +
If it's just the coil, you're looking at roughly £40 to £100 for the part on most mainstream cars and around 20 minutes of labour, so a typical independent garage bill lands somewhere in the £80 to £150 range. A main dealer will charge more for both, easily double on the labour. Wiring or connector repairs are usually cheap parts but fiddly to trace, so the cost is in the diagnostic time. If it turns out to be the ECU driver circuit, that's the painful one, often several hundred pounds once you factor in the unit and programming.
How do I know if it's the coil or something else on my car? +
The swap test settles it nine times in ten. Move the cylinder 6 coil to another cylinder, clear the code, and drive. If the misfire follows the coil to its new home, the coil is dead. If the fault stays on cylinder 6 with a different coil fitted, you're chasing wiring, the connector, or the spark plug instead. Check the plug while you're in there, it's quick and they often go hand in hand.
Can I just replace the coil myself? +
On a coil-on-plug engine, yes, this is one of the more approachable jobs. The coil sits on top of the cylinder, held by one or two bolts and a connector. Disconnect the battery, unclip the plug, undo the bolt, pull the old coil and fit the new one. Buy a decent branded coil rather than the cheapest one going, the no-name units tend to fail again within a year. Wiring faults or anything pointing at the ECU is a different story and best left to a garage.
If I just clear the code, will it stay gone? +
Only if the actual fault has fixed itself, which it won't. Clear it with a dead coil still fitted and it'll be back within a few miles, often before you've left your road. Worse, every mile you drive with that cylinder misfiring is pumping raw petrol into the catalytic converter, and replacing a cat costs a great deal more than a coil. Fix the cause, then clear the code.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →