P0350
PowertrainIgnition Coil Primary/SecondaryCircuit
P0350 means the ECU has spotted an electrical fault in the ignition coil circuit, either on the primary (low voltage) side or the secondary (high voltage) side that fires the plug. For you the driver, that usually shows up as a misfire and a flashing or steady engine light, and the engine may drop into limp mode to protect itself. It's a generic coil-circuit code rather than one pointing at a specific cylinder, so it tells you something's wrong with the ignition wiring or a coil, just not exactly which one without a bit of digging.
ⓘ Information only. This page provides general educational information about fault code P0350. 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 P0350 mean?
P0350 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Ignition Coil Primary/SecondaryCircuit.
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 the misfire is bad
- • Rough, lumpy idle that smooths out then gets worse again
- • Hesitation or a flat spot when you put your foot down
- • Hard starting, and on a cold morning it may take a few cranks to catch
- • Stalling at junctions or when the engine drops to idle
- • Fuel economy noticeably down because the cylinder isn't burning cleanly
Possible causes
Causes commonly associated with P0350, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. A failed or failing ignition coil. This is the usual culprit, coils get hot, get old, and eventually break down internally
- 2. Damaged or corroded wiring and connectors at the coil. Heat and vibration crack the insulation and the pins go green over time
- 3. Worn or fouled spark plugs putting extra strain on the coil, which can drag a marginal coil over the edge
- 4. A poor engine earth or corroded ground strap, which messes with the coil's control circuit
- 5. A blown fuse or dead relay feeding the ignition system, killing the supply to one or more coils
- 6. Low system voltage from a tired battery or a failing alternator, which can upset coil operation
- 7. A faulty driver circuit inside the PCM. Uncommon, but it does happen when nothing 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. Read the codes and freeze-frame data first. If you also see a cylinder-specific code like P0351 or P0352 stored alongside, that narrows you straight down to the offending coil
- 2. Pull the coil connectors and look properly. Check for corroded pins, melted plastic, chafed wiring, and a loose or cracked connector. A surprising number of these are just a dodgy plug
- 3. With the ignition on, check you've got battery voltage at each coil connector. No supply points you at fuses, relays, or the feed wiring rather than the coil itself
- 4. Measure primary and secondary resistance on the coils with a multimeter and compare against the manufacturer's figures. An open or shorted winding shows up here
- 5. Swap a suspect coil with a known-good one from another cylinder, clear the code, and see if the fault follows the coil. Cheapest reliable test there is
- 6. If coils, wiring, and supply all check out, look at the PCM ground pulse on the scope before condemning the module. Don't replace a PCM on a hunch
Common questions about P0350
Are the cheap coils off eBay any good or should I pay for proper ones? +
For most everyday cars a decent branded aftermarket coil from the likes of Bosch, NGK, or Delphi does the job fine and costs a lot less than main-dealer parts. The trouble is the no-name bargain coils, they often fail within months and you're back where you started, sometimes with a new P0350. If your car runs individual coil-on-plug units it's often sensible to do them in a set if the others are the same age and mileage. Avoid the £8 specials, they're a false economy.
Can I keep driving it like this? +
Short trips to get home or to a garage are usually alright, but I wouldn't make a habit of it. A misfire dumps unburnt fuel into the exhaust, and sustained misfiring will cook your catalytic converter, turning a cheap coil job into an expensive cat job. If the engine light is flashing, that's the ECU telling you the misfire is bad enough to do damage, so ease off and get it sorted soon. Stalling at a busy junction is the real safety worry.
Is this going to be an MOT fail? +
The code on its own isn't a direct fail, but if the engine warning light is lit when the tester plugs in or eyeballs the dash, that's an automatic MOT failure under current rules. A live misfire can also push your tailpipe emissions over the limit, which fails the emissions side of the test. Fix the fault, clear the light, and drive a few cycles so it doesn't come straight back before you book it in.
What's it likely to cost to put right? +
If it's a single coil, you're looking at roughly £40 to £120 for the part and around an hour's labour at an independent, so most jobs land somewhere in the low hundreds all in. A main dealer will charge more for both parts and labour and could push it towards £200 to £300 for one coil. Wiring or connector repairs can be cheaper if it's just a clean-up and reterminate. A PCM replacement is the worst case and can run into four figures with programming, but that's rare with this 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 →