P0351: Ignition Coil A Primary/Secondary Circuit
P0351 is a powertrain diagnostic trouble code in the ignition system or engine misfire group. Our vehicle database stores it against 1 model.
What P0351 actually means
Only 1 model in our database record P0351, a powertrain code in the ignition system or engine misfire group — a narrower fault than the generic codes, which makes the model list below unusually informative.
The stored definition for P0351 is “Ignition Coil A Primary/Secondary Circuit”. The first character of the code identifies the system — Powertrain in this case. The second character tells you who defined the code: this one is a generic code defined by SAE J2012 and shared by every manufacturer. Reading the code that way matters: a generic code tests the same underlying condition on almost every vehicle, so the causes below apply broadly across makes.
Within that system, P0351 sits in the ignition system or engine misfire group. That is the part of the vehicle the control module was watching when it set the code — the ignition components and combustion itself — coils, plugs, and the crank and cam position signals — and it narrows down enormously where a technician will start looking. Misfire diagnosis leans on per-cylinder misfire counters and freeze-frame data, which point at one cylinder instead of the whole engine.
What makes P0351 easy to get wrong. A coil-specific misfire code points at the coil serving that cylinder, and the swap test settles it in minutes: move the coil to another cylinder and see whether the code follows. If the code stays, the fault is in the coil’s control circuit or its driver, not the coil.
How serious is P0351?
We rate P0351 as Moderate — diagnose soon. That rating comes from the severity recorded in our database for this code, not from how alarming the name sounds.
A moderate-severity code usually leaves the vehicle drivable, but the underlying fault tends to worsen and can cascade into a more expensive repair. It is reasonable to drive cautiously to a workshop in the near term, but the code should be diagnosed rather than cleared and forgotten.
Most likely causes of P0351
Our database records a single cause for P0351, reported by the 1 model that log it.
Ignition coil pack failure on cylinder 1 — recorded on every model that logs this code.
Causes are listed as recorded in the database. The same code can have different root causes on different vehicles, so the ranking is a starting order for diagnosis rather than a diagnosis in itself.
How a technician diagnoses P0351
Diagnosis for P0351 follows the same logic as any stored powertrain code: confirm the code is active rather than historic, then work through the ranked causes from cheapest and most likely to most intrusive. In practice that means:
How a technician works P0351 — decision path
Powertrain codes respond to data. Capture the freeze frame, then work through the ranked causes from cheapest and most likely to most intrusive.
- Confirm the code is active and capture freeze-frame dataThe snapshot recorded when the code set holds the engine speed, load, coolant temperature and fuel trims at that moment — often the single most useful piece of evidence for separating one candidate cause from another.
- Compare live data against the freeze frameRe-create the conditions from the snapshot and watch the relevant sensors live. A value that cannot reach the expected range narrows the search immediately.
- Work the ranked causes from cheapest and most likelyThe list on this page is ordered by how many of the recorded vehicles show each cause. Start at the top: an intake leak, a dirty sensor or a worn cap is far more common than a failed assembly.
- Repair the confirmed cause, then re-check the monitorsFix what the evidence actually points at rather than replacing parts speculatively — a misfire or lean code will re-set if the real cause is still present.
- Clear the code and complete a full drive cycleClearing alone proves nothing. The code must stay clear through a drive cycle that reproduces the original conditions, and the readiness monitors must run again.
If a workshop replaces a component for P0351 without showing you the measurement that condemned it, ask for the data. On a ignition system or engine misfire code, the recorded causes are usually testable, so a diagnosis should be demonstrable rather than asserted.
What drives the cost of fixing P0351
We deliberately do not print a single repair price for P0351. Ignition repairs are usually modest per cylinder, but a misfire left alone can turn into a catalytic-converter bill. The honest answer is that the cost is set by which cause is actually present, and that range is wide — a repair for the first cause listed above and the last can differ by more than an order of magnitude in parts alone: a coil and a catalytic converter are not the same job, and the second one arrives if the first is ignored. Add regional labour rates and the spread becomes wider still.
The factors that actually move the number, in rough order of impact:
- Catching it before the catalyst dies. A misfire driven long enough destroys the catalytic converter, turning a coil-and-plug repair into the most expensive job in this group.
- Coil and plug access. A transverse V6 can double the labour of an inline-4 for identical parts, purely because of where the coils sit.
- Compression testing. When the swap test implicates the cylinder itself, a leak-down test is a different job with its own charge.
- Diagnosis billed separately. Misfire diagnosis is measurement-heavy, so the diagnostic line item matters more here than on most codes.
The practical approach: get the cause confirmed first, then collect two or three written quotes for that specific repair. To judge whether the repair is worth doing against the value of the vehicle, use our repair-or-replace decision guide.
Vehicles in our database that log P0351
Only 1 model in our database record P0351, so the list below is short but specific. The makes appearing most often are Toyota (1). Each model links to its own guide, where this code appears alongside that vehicle's full fault list and running costs.
Frequently asked questions about P0351
What does the P0351 code mean?
P0351 is a powertrain trouble code meaning "Ignition Coil A Primary/Secondary Circuit". It belongs to the ignition system or engine misfire group of the SAE J2012 numbering scheme, and it is a generic code defined by SAE J2012 and shared by every manufacturer. The code is set by the powertrain control module when the monitored system reports a value outside its expected range.
Why is my check-engine light flashing with P0351?
A flashing check-engine light means a misfire is happening right now, and the raw fuel passing through the exhaust can destroy the catalytic converter within a short distance. Stop driving and have the vehicle recovered rather than continuing to a workshop under power.
What are the most common causes of P0351?
In our vehicle database, the causes recorded for P0351 are: Ignition coil pack failure on cylinder 1. They are ranked on the page by how many of the 1 vehicles that log this code list each cause.
How much does it cost to fix P0351?
We do not publish a single figure for P0351 because the real cost depends entirely on which cause is present — a repair for the cheapest cause on the list and the most expensive one differ by an order of magnitude, and labour rates vary by region. The page explains which factors drive the cost and recommends collecting written quotes before authorising work.
Which vehicles commonly report P0351?
Our database stores P0351 against 1 vehicles, most frequently from Toyota (1). The full list is shown on this page and each model links to its own cost and fault guide.
Related codes and next steps
Codes that share the same system group often appear together, because a single fault can set more than one:
For the full list, see the OBD-II fault code cross-reference. If the repair cost is what you are weighing, model the total with our total cost of ownership calculator before deciding, and check whether an open safety recall covers the fault with the recall lookup.
Sources and scope
Code definitions follow SAE J2012 / ISO 15031-6 naming. The descriptions, listed causes, and severity ratings on this page are the values stored in the VehCalc vehicle database (snapshot 2026-08-20) for the models listed above. Codes and causes vary by model year and engine.
Diagnostic reference only — not repair advice. This page is provided for educational and planning purposes and does not replace an inspection by a qualified technician or the manufacturer's service information. Before repairing a vehicle you depend on, confirm the diagnosis with an ASE-certified mechanic.