fault code guide
P0351: Ignition Coil 'A' Primary/Secondary Circuit Malfunction
The engine computer has detected an electrical circuit failure at the ignition coil for cylinder one. This causes the engine to misfire, hesitate during acceleration, and burn excessive petrol.
How it shows up: The amber engine management light will illuminate on your dashboard, and it will flash if the engine is misfiring heavily. You will typically notice engine shuddering at idle, sluggish throttle response, and the code P0351 stored on an OBD scanner.
Updated 9 November 2026
Can I keep driving?
Service soon
Driving for extended periods with an active misfire can quickly melt and destroy your expensive exhaust catalytic converter with raw petrol.
What to do right now
- 1Pull over and stop driving if the engine management light starts flashing, as this indicates a severe catalyst-damaging misfire.
- 2Switch off the engine to protect the exhaust system and allow under-bonnet components to cool down.
- 3Check your instrument cluster for any additional warnings such as high coolant temperature or low oil pressure.
Likely causes
Most likely first.
- Likely
Failed ignition coil
The internal electrical windings inside the cylinder one coil break down from heat and vibration, disrupting the circuit and stopping spark generation.
- Possible
Damaged coil wiring or connector
The plastic locking clip on the coil plug can snap off, allowing vibration to loosen electrical pins or causing wires to crack near the connector.
- Possible
Severely worn spark plug
An excessively wide spark plug gap puts high electrical resistance on the secondary ignition circuit, stressing the coil until it fails.
- Rare
Faulty engine control unit driver
The internal transistor within the engine computer that switches the coil ground circuit on and off can burn out or suffer an internal short.
What you can check yourself
Park somewhere safe and level, engine off, before you start.
- 1
Check the cylinder 1 coil electrical plug
With the engine switched off and cool, locate the ignition coil on cylinder one, which is closest to the engine timing belt or chain. Press firmly on the wiring connector to make sure it is fully seated and that the plastic locking clip is not broken.
- 2
Inspect the wiring harness for damage
Examine the exposed wires leading into the coil connector for frayed insulation, chafing against the engine block, or rodent bite marks. Gently wiggle the wires to see if any terminal feels loose inside the plastic plug.
- 3
Inspect for oil or moisture ingress
Unbolt the coil and lift it out of the spark plug well. If the rubber boot is soaked in engine oil from a leaking rocker cover gasket or pooled with water, this can ground out the high-voltage spark before it reaches the plug.
Rough cost to fix
Rough estimateTypical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. Prices depend mainly on whether your car uses individual pencil coils for each spark plug or an integrated multi-cylinder coil pack that must be replaced as one unit.
Replace cylinder 1 ignition coil
- Do it yourself
- €40–120£35–105 in the UK
- At a garage
- €110–240£95–210 in the UK
Replace a full set of spark plugs
- Do it yourself
- €30–90£25–80 in the UK
- At a garage
- €90–190£80–165 in the UK
Repair damaged coil connector and wiring
- Do it yourself
- Garage job
- At a garage
- €85–180£75–155 in the UK
When to go to a garage
- The engine management light begins flashing steadily while driving.
- Fitting a replacement ignition coil does not clear the fault code or the engine misfire.
- You smell raw, unburnt petrol around the vehicle or observe smoke exiting the exhaust pipe.
- The electrical wiring harness appears melted, severed, or heavily corroded.
Questions drivers ask
Can I drive with fault code P0351?
You should only drive short distances at low engine speeds to reach a place of repair. If the engine management light flashes, you must pull over and call for roadside assistance immediately. Continuing to drive with an unburnt fuel mixture being pumped into the exhaust will destroy the catalytic converter in a matter of minutes.
What does Ignition Coil 'A' mean?
Coil 'A' refers to the primary ignition circuit for cylinder number one. On most straight-four engines, cylinder one is positioned closest to the front of the engine where the accessory drive belts and timing chain are located. Consult your vehicle handbook to verify cylinder numbering for your specific engine layout.
Will clearing the P0351 code fix the problem?
Clearing the code with a scan tool only turns off the dashboard warning light temporarily. If the coil is degraded or the circuit is broken, the engine computer will detect the missing electrical signal within seconds of starting the engine and trigger the light again. The underlying hardware fault must be physically repaired.
Will P0351 cause my car to fail its NCT or MOT?
On the UK MOT, a lit engine management light is an automatic fail for petrol cars registered from July 2003. On the Irish NCT, an engine warning light or an electrical fault code results in an Advisory Pass on its own, but the car will fail if the misfire causes tailpipe exhaust emissions to exceed legal testing limits.
Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.
The warning light you may see
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General guidance for most cars, not a diagnosis of yours. Details differ by make, model and year - check your handbook, and if in doubt, don't drive.