P0355
PowertrainIgnition Coil"E" Primary/Secondary Circuit
This is an electrical fault in the ignition coil circuit for cylinder 5, the one the ECU labels coil 'E'. Either the coil itself, its plug, or the wiring back to the ECU isn't behaving electrically, so the spark for that cylinder is unreliable or missing. For you that usually shows up as a misfire you can feel, a warning light, and an engine that runs rough until you sort the coil or its connector.
ⓘ Information only. This page provides general educational information about fault code P0355. 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 P0355 mean?
P0355 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Ignition Coil"E" 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 on, sometimes flashing if cylinder 5 is dropping out badly
- • A clear misfire or stumble, worst when you put your foot down or pull away from a junction
- • Lumpy idle with a vibration coming up through the pedals and seat
- • Down on power, especially noticeable going up a motorway slip road
- • Worse fuel economy because the unburnt mixture from cylinder 5 is being wasted
- • The odd stall when coming to a stop, particularly when the engine is cold
Possible causes
Causes commonly associated with P0355, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. A failed ignition coil for cylinder 5. Coil-on-plug units cook themselves over time and this is where most P0355s end up
- 2. Corroded or loose terminals in the coil connector. Heat and damp under the bonnet get into these plugs and the contact goes intermittent
- 3. A break or short to earth in the wiring between the coil and the ECU, often where the loom rubs or flexes near the engine
- 4. A knackered or fouled spark plug in cylinder 5 that's loaded the coil and pushed the circuit out of range
- 5. A poor engine earth or a tired ground strap, which can make the coil driver readings go haywire
- 6. An intermittent wiring fault that only shows when the engine moves on its mounts, so it comes and goes
- 7. A failed coil driver inside the PCM. Rare, and the last thing to suspect once everything else checks out
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. Pull all the codes first and see what's sitting alongside P0355. A misfire code like P0305 next to it points you straight at cylinder 5 and tells you the spark is actually missing, not just an electrical glitch
- 2. Unplug the coil connector and have a proper look. Green corrosion, spread terminals, oil or coolant in the plug, a melted connector body. Plenty of these are fixed at the connector before you ever buy parts
- 3. Swap the cylinder 5 coil with a known-good one from another cylinder, clear the code and drive it. If the fault jumps to the cylinder you moved the coil to, the coil is your problem
- 4. Measure the coil's primary and secondary resistance against the workshop figures, and confirm you've got battery voltage feeding the coil with the ignition on
- 5. Check continuity from the coil connector back to the ECU for an open, and check the trigger wire for a short to earth, wiggling the loom while you watch for it to drop in and out
- 6. If the coil, plug and wiring all come back clean, then look at the PCM driver output for cylinder 5. Don't go here until you've ruled out everything cheaper
Common questions about P0355
What am I likely to pay to get this fixed? +
If it turns out to be the coil, which it often does, an independent garage will usually have you sorted for somewhere in the low three figures including a new coil and a spark plug for that cylinder. Many people get away cheaper because the coils are quick to reach on most engines. Wiring repairs or PCM driver work cost more and need more labour time, so expect mid three figures. A main dealer will charge a fair bit more for the same coil thanks to their hourly rate, so an independent is the sensible first call here.
How do I know if it's the coil or the wiring on my car? +
The coil swap is the quickest answer. Move the cylinder 5 coil to a neighbouring cylinder, clear the code and run it. If the fault follows the coil to its new home, the coil is dead and you can buy with confidence. If P0355 stays on cylinder 5 after the swap, the coil is fine and you're looking at the connector or the wiring back to the ECU. Inspect the plug and terminals before anything else, because a dirty or spread connector is cheap to fix and catches a lot of people out.
Can I just change the coil myself? +
On most coil-on-plug setups, yes. The coil sits on top of the spark plug, held by a single bolt and a plug connector, so it's often a five minute job once you've worked out which one is cylinder 5. Buy a decent branded coil rather than the cheapest one going, replace the spark plug while you're in there, and give the connector a clean. Where it stops being a DIY job is when the fault is in the loom or the PCM, because tracing that needs test gear most people don't own.
If I just clear the code, will it stay gone? +
Only if you've actually fixed what caused it. Clear it with a healthy coil and tight connector and it should stay off. Clear it and carry on with a failing coil and it'll come straight back, usually within a few miles or the next cold start. If the cause is an intermittent wiring fault, the light can clear and then return days later when the engine vibrates the wire just right, which is the frustrating one to pin down. Don't keep clearing it and driving, because a dead cylinder dumping fuel can wreck the catalytic converter.
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 →