P0351 Code: Ignition Coil A Primary/Secondary Circuit

What Does P0351 Mean?

P0351 is the generic OBD-II code for “Ignition Coil ‘A’ Primary/Secondary Circuit”. The engine computer fired, or tried to fire, ignition coil A and did not see the electrical response it expects from that coil’s circuit. It is a circuit fault in the coil’s wiring, control or feedback, not a measurement of misfiring.

Every coil has a low-voltage primary winding and a high-voltage secondary winding. When the computer switches the primary off, the collapsing field induces tens of thousands of volts in the secondary to fire the plug. How the computer monitors this depends on the design:

• Two-wire coils: the computer’s driver switches the primary to ground and watches the current. No current, or far too much, sets the code.
• Three- and four-wire coils with a built-in igniter: the computer sends a low-voltage trigger and the igniter does the switching. Toyota and Lexus call the trigger IGT and the coil’s reply IGF; IGT without a valid IGF sets P0351.

The family runs from P0351 (coil A) to P0362 (coil L); GM words P0351 as “Ignition Coil 1 Control Circuit”.

What Are the Symptoms of P0351?

P0351 symptoms depend on whether coil A has stopped firing completely or only drops out now and then. A dead coil gives a constant misfire on one cylinder; an intermittent connector fault may set the code with almost nothing to feel, perhaps only over bumps or in wet weather.

• Check engine light on, and flashing under load if the misfire is severe enough to threaten the catalytic converter.
• Rough idle and shaking — one cylinder down is easy to feel at a standstill; see car shakes at idle.
• Hesitation and loss of power, worst under load.
• A misfire code alongside it, usually P0301 or P0300.
• A fuel smell from the exhaust and worse fuel economy.

What Causes P0351?

P0351 is caused by a fault in coil A’s connector, wiring or the coil itself far more often than by the engine computer. The coil circuit lives on a hot, vibrating engine and is disturbed every time the plugs are changed. Check the cheap, common causes first, in this order:

1. Coil connector and locking tab — not fully seated, a broken tab that lets it work loose, or corroded and spread terminals. Classic after spark plug work.
2. Harness damage or chafing — insulation rubs through on brackets or the valve cover, cracks with heat, or is chewed by rodents.
3. Failed ignition coil — an open or shorted primary winding, a cracked body, or a failed built-in igniter. Oil in the plug well and heat speed this up.
4. Coil power feed fuse or relay — usually shared by all the coils, so a blown fuse normally brings P0351 together with P0352 and the other coil codes, and often a no-start.
5. Engine computer driver — rare, usually after a shorted coil or wire overloaded it. Prove the coil and wiring good first.

How Do You Diagnose P0351?

Diagnosing P0351 usually takes 30-90 minutes with a scan tool, a digital multimeter and the wiring diagram for your engine. The goal is to find out whether the coil, its wiring or its control signal is at fault before buying parts. Work with the engine off unless a step says otherwise.

1. Record every code and the freeze frame (5 minutes)

P0351 alone points to coil A or its own wiring; several coil codes together point to something shared — a fuse, power feed, ground or a shared feedback line.

2. Inspect the connector and harness (10 minutes)

Unplug coil A, look for corrosion, pushed-back pins or a broken locking tab, and follow the harness for rubbed insulation. Reconnect until the latch clicks.

3. Swap coil A with a neighbouring coil (15 minutes)

If the code moves with the coil (for example to P0352), the coil is bad; if P0351 stays, suspect the wiring or control signal. The method is in our guide on how to tell if an ignition coil is failing.

4. Check power and ground at the connector (10 minutes)

Key on, the power terminal should read battery voltage, about 12 V. A drop above about 0.2 V from the ground terminal to battery negative while cranking means a poor ground.

5. Measure primary resistance on two-wire coils (10 minutes)

Most two-wire coils read roughly 0.4-2 Ω across the primary pins; OL (open) or a near-zero short condemns the coil. Use your engine’s figure, and skip this on three- and four-wire coils — a built-in igniter cannot be ohm-tested meaningfully.

6. Confirm the trigger signal (advanced)

On coils with a built-in igniter the trigger is a low-current signal of roughly 5 V. Do not probe it with a test light or noid light — they load the circuit and can damage the computer’s driver. An oscilloscope comparing coil A with a healthy coil is the right tool.

How Do You Fix P0351 and What Does It Cost?

Fixing P0351 means repairing whichever part of coil A’s circuit the tests condemned — most often a connector, a chafed wire or a single coil, and rarely anything above a few hundred dollars. Typical US costs, October 2026 — varies by vehicle and region:

Rear coils on transverse V6 engines can need the intake plenum removed, adding labour. Replace a worn or oil-soaked plug at the same time; see how often to replace spark plugs.

What doesn’t work: clearing the code without a repair, fitting a full set of coils for one wiring fault, or replacing the computer first.

How Is P0351 Different From P0301 and P0300?

P0351 and P0301 often appear together but measure different things. P0351 is a circuit code: the computer saw an electrical fault in coil A’s control or feedback. P0301 is a misfire code: crankshaft speed showed that cylinder 1 is not producing power, whatever the reason.

P0351 with P0301 points to the ignition side. P0301 alone leaves the plug, injector and compression in play, because a coil can pass the circuit check yet still give a weak spark.

Which Cylinder Is Ignition Coil A?

Ignition coil A is usually the coil for cylinder 1, so P0351 normally pairs with cylinder 1, P0352 with cylinder 2 and so on. The letter-to-cylinder mapping is set by the manufacturer, however, not by the generic code, so confirm it in the service information for your engine.

Two situations break the simple rule. On older waste-spark systems one coil fires two cylinders, so “coil A” may serve a pair. And on V6 and V8 engines cylinder 1 can be on either bank, following the manufacturer’s own numbering.

Is P0351 Serious?

P0351 is moderately serious: it rarely harms the engine itself, but a coil that stops firing sends unburned fuel into the exhaust, where it burns inside the catalytic converter. Weeks of that can turn a $150 coil repair into a converter replacement.

A damaged converter often shows up later as P0420, a rattle or a rotten-egg smell. With a steady light and smooth running it is not an emergency, but fix it within days.

Can I Drive With P0351?

You can usually drive gently for a short distance with P0351 if the check engine light is steady and the engine runs acceptably. If the light is flashing, the engine shakes hard or power drops sharply, stop driving at load and arrange the repair before longer trips.

When Should You See a Mechanic?

See a mechanic for P0351 when the code stays with the cylinder after a swap but you cannot find a wiring fault, when several coil codes appear together, when a fuse keeps blowing, or when coil A sits under the intake manifold. Signal faults need wiring diagrams and an oscilloscope more than parts. More ignition codes are in our trouble codes section.

Frequently Asked Questions