# P0351: Ignition Coil "A" Primary/Secondary Circuit **Verdict:** Drive to a shop this week Ignition and misfire - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $150-$500 - **Urgency:** This week - **Most likely:** Failed ignition coil for cylinder 1 - **DIY?:** Yes, on most engines ## Quick answer P0351 means the engine computer has found a problem in the circuit for ignition coil "A", which on most engines is the coil for cylinder 1. The computer is not seeing the expected electrical response when it fires that coil. A failed coil is the most common reason, followed by a wiring or connector problem. ## What does P0351 mean? An ignition coil turns 12-volt battery power into the tens of thousands of volts needed to fire a spark plug. The engine computer, or a separate igniter, switches the coil's primary winding on and off; when it switches off, the collapsing magnetic field fires the plug through the secondary winding. Most modern engines use one coil per cylinder, mounted right on top of the plug. P0351 is a circuit code for coil "A". The computer watches the primary circuit for the expected current or a feedback signal, and sets the code when it sees an open, a short or no response. On most engines coil A fires cylinder 1, but on some waste-spark systems it is a coil pack serving a pair, such as cylinders 1 and 4. On many vehicles the code can set on the first trip, and it often appears with misfire code P0301. ## What are the symptoms of P0351? - Check engine light on - Engine shakes or runs rough, especially at idle - Loss of power when accelerating - A misfire code for cylinder 1 (P0301) may also appear ## What causes P0351? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed ignition coil** (most common). The coil's windings can short or open after years of heat and vibration, or its body can crack. A failing coil may still fire weakly, causing a misfire under load, or stop completely. Swapping the cylinder 1 coil with a neighbor and seeing the code change to that coil's letter, such as P0352 for coil B, confirms it. 2. **Damaged wiring or loose coil connector** (common). Coil connectors become brittle with engine heat, and their locking tabs often break during spark plug work, leaving a connector that vibrates loose. Corroded pins, a wire chafed against the valve cover, or rodent damage cause the same fault. Inspect the coil A connector and harness for a loose fit, broken tab or green corrosion on the pins. 3. **Bad coil power or ground circuit** (less common). Coils share a power feed through a fuse or relay and a common ground. A blown fuse, failing relay, corroded ground or low voltage can affect coil A, but usually other coils too, setting several codes at once. A shop checks for battery voltage at the coil connector with the key on and confirms the ground is clean and tight. 4. **Engine computer driver fault** (rare). On many engines the computer itself contains the driver transistor that switches each coil. A shorted coil drawing too much current can damage that driver, so a new coil does not fix the code. This is rare and confirmed only after the coil and wiring test good. Replace the shorted coil before installing a new or repaired computer. ## How do you diagnose P0351? 1. Read all codes. P0351 with P0301 points to cylinder 1. Several coil codes together point to a shared power or ground problem. 2. Check the coil connector for damage and make sure it clicks firmly into place. 3. Swap the coil with another cylinder, clear codes, and see if the code changes to that coil's number. 4. Test coil power, ground, and the control signal with a meter or scope if swapping does not move the fault. ## How do you fix P0351, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace ignition coil | $150-$400 | Includes one coil and labor. Rear-bank coils on some V6 engines cost more to reach. | | Repair coil wiring or connector | $100-$300 | Replace a cracked connector or repair damaged wires. | | Replace or repair the engine computer | $600-$1,500 | Rare. Only after the coil and wiring test good. Replace the shorted coil first so the new computer is not damaged. | Full price breakdowns: [ignition coil replacement cost](/cost/ignition-coil-replacement), [spark plug replacement cost](/cost/spark-plug-replacement). ## Is it safe to drive with P0351? > **Drive to a shop this week.** You can usually drive gently to a shop. If the check engine light starts flashing, the misfire is severe and can damage the catalytic converter, so stop driving hard. ## Will P0351 fail an emissions test? P0351 with the check engine light on fails an OBD-based emissions test. If the coil fault causes a cylinder 1 misfire, tailpipe hydrocarbons rise and the catalytic converter is at risk; some engines shut off that cylinder's injector to protect it. After the repair, drive for several days so the readiness monitors complete before testing. ## After the repair: clearing P0351 Clear the code and start the engine, checking that it idles smoothly with no shake. Make sure the coil connector is fully latched and its locking tab engaged. Drive under load and watch the cylinder 1 misfire counter if your scan tool shows it. If neither P0351 nor P0301 returns over a week of driving, the repair held. ## How to prevent P0351 - Replace spark plugs on schedule; worn plugs force coils to work harder and fail sooner. - Press coil connectors until they click, and check locking tabs after any plug work. - Keep oil out of the plug wells by fixing valve cover leaks promptly. - Avoid pressure-washing the engine bay directly over coils and their connectors. ## Codes often seen with P0351 - [P0301](/codes/p0301): Cylinder 1 Misfire Detected - [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected - [P0306](/codes/p0306): Cylinder 6 Misfire Detected ## Frequently asked questions ### Which coil is ignition coil A? On most engines, coil A is the coil for cylinder 1, and coils B, C and so on follow cylinder number. On some waste-spark systems, coil A is a pack that fires a pair of cylinders. Check your service information to confirm, since a few manufacturers number coils differently. ### Can I replace an ignition coil myself? Yes, on most coil-on-plug engines it is one bolt and one connector, and the job takes minutes. Coils under the intake manifold on some V6 engines are harder and may be worth a shop visit. Make sure the new coil's connector clicks fully into place before you start the engine. ### Should I replace the spark plug when I replace the coil? It is a good idea if the plugs are old, since a worn plug with a wide gap puts extra strain on the coil. That strain can make a new coil fail sooner. If the plugs are due, replace the full set at the same time, since the coils are already off. ### How much does it cost to fix P0351? Most P0351 repairs cost $150 to $400 for a new ignition coil, including labor, at an independent shop. Repairing a cracked connector or damaged wire costs $100 to $300. A computer driver failure is rare but costs $600 to $1,500, so the shop should confirm the coil and wiring first. ### Can I drive with P0351? Usually yes, gently, for a short distance to a shop. If coil A has failed completely, cylinder 1 is not firing, so the engine will shake and lose power. A flashing check engine light means the misfire is severe enough to damage the catalytic converter, so avoid hard driving. ### What is the difference between P0351 and P0301? P0351 is an electrical fault in the coil A circuit, while P0301 means cylinder 1 is misfiring for any reason. P0301 alone could be a plug, injector or compression problem. When both appear together, the coil or its wiring is the likely cause, because the circuit fault explains the misfire. ### Why do I have P0351 and other coil codes at the same time? Several coil codes together, such as P0351, P0352 and P0353, usually point to something shared rather than several failed coils. A blown fuse, failing relay, poor ground or low system voltage can affect all coils at once. Check the coil power fuse and battery voltage before replacing any coils. ### Do I need to replace all the ignition coils? No, replace only the coil that tests bad unless others are also failing. Coils usually fail one at a time. On a high-mileage engine with original coils, some owners replace them all to avoid repeat visits, but that is a cost choice, not a requirement for fixing P0351. ### Will P0351 pass inspection? No, P0351 with the check engine light lit fails an OBD-based emissions inspection. After the coil or wiring is repaired, clear the code and drive normally for several days so the readiness monitors complete. Check them with a scan tool before returning, to avoid a wasted trip. ### Can a bad coil damage the engine computer? It can, though it is uncommon. A coil with shorted windings can draw too much current through the computer's driver circuit and damage it. That is why a shop replaces the shorted coil first, then confirms the driver works before deciding whether the computer also needs repair. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## Other ignition and misfire codes - [P0332 Knock Sensor 2 Circuit Low (Bank 2)](https://diagxcar.com/codes/p0332) - [P0335 Crankshaft Position Sensor "A" Circuit](https://diagxcar.com/codes/p0335) - [P0336 Crankshaft Position Sensor "A" Circuit Range/Performance](https://diagxcar.com/codes/p0336) - [P0339 Crankshaft Position Sensor "A" Circuit Intermittent](https://diagxcar.com/codes/p0339) - [P0340 Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0340) - [P0341 Camshaft Position Sensor "A" Circuit Range/Performance (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0341) - [P0344 Camshaft Position Sensor "A" Circuit Intermittent (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0344) - [P0345 Camshaft Position Sensor "A" Circuit (Bank 2)](https://diagxcar.com/codes/p0345) - [P0352 Ignition Coil "B" Primary/Secondary Circuit](https://diagxcar.com/codes/p0352) - [P0365 Camshaft Position Sensor "B" Circuit (Bank 1)](https://diagxcar.com/codes/p0365) - [P0301 Cylinder 1 Misfire Detected](https://diagxcar.com/codes/p0301) - [P0306 Cylinder 6 Misfire Detected](https://diagxcar.com/codes/p0306) - [P0320 Ignition/Distributor Engine Speed Input Circuit](https://diagxcar.com/codes/p0320) ## Symptoms - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) ## Repair costs - [Ignition coil replacement cost](https://diagxcar.com/cost/ignition-coil-replacement): $150-$400 - [Spark plug replacement cost](https://diagxcar.com/cost/spark-plug-replacement): $120-$450 --- Source page: https://diagxcar.com/codes/p0351 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.