Ignition & misfire · Powertrain · generic (SAE-defined)
P0351: Ignition Coil "A" Primary/Secondary Circuit
P0351 means the engine computer detected a fault in the primary or secondary circuit of ignition coil "A", which often fires cylinder 1 on coil-on-plug engines.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0351 sets
The powertrain control module (PCM) switches each ignition coil on and off and monitors the coil control circuit for the expected electrical response. P0351 sets when coil "A" shows an open, short, or abnormal current or feedback signal. On many engines coil "A" corresponds to cylinder 1, but assignments vary by manufacturer.
Common causes of P0351
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Failed ignition coil "A"
- Open or shorted coil control wiring
- Loose, corroded, or damaged coil connector
- Loss of power feed to the coil
- Faulty spark plug or boot causing excess secondary load
- Rarely, a PCM driver fault
P0351 symptoms
- Check engine light on or flashing
- Misfire in the affected cylinder
- Rough idle and hesitation
- Reduced power and fuel economy
How P0351 is diagnosed
- Check freeze frame data and look for matching misfire codes such as P0301.
- Confirm which cylinder coil "A" serves in service information.
- Inspect the coil connector and wiring for damage or corrosion.
- Swap coil "A" with another coil and see if the code moves.
- Check coil power supply and control circuit with a multimeter or test light.
Typical fixes for P0351
- Replace ignition coil "A"
- Repair coil wiring or connector
- Replace spark plug and boot if damaged
- Repair the coil power feed circuit
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0351 FAQ
What does code P0351 mean?
P0351 means the engine computer detected a fault in the primary or secondary circuit of ignition coil "A", which often fires cylinder 1 on coil-on-plug engines. The standard definition is "Ignition Coil "A" Primary/Secondary Circuit."
Can I drive with a P0351 code?
Only gently and for a short distance. A failed coil causes a misfire, and if the check engine light flashes, stop driving soon to avoid catalytic converter damage.
Is coil A always cylinder 1?
Often, but not always. On waste-spark systems, one coil can fire two cylinders, so check service information.
Should all coils be replaced if one fails?
Not necessarily. Replacing only the failed coil is common, though some owners replace all of them on high-mileage engines to prevent repeat issues.
Keep researching
Engine guides by brand (known issues, specs)
More ignition & misfire codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.