P0351
Ignition Coil A Primary/Secondary Circuit
If your code reader dashboard displays the generic DTC error code P0351, your vehicle is currently experiencing an active failure related to "Ignition Coil A Primary/Secondary Circuit". Proper system troubleshooting is required to safely clear this warning.
Driver's Summary
Storing code P0351 is your car's way of telling you something is wrong with the ignition coil a primary/secondary circuit. You may notice engine misfire, rough idle, lack of power, all of which are direct consequences of this malfunction. This is a serious fault — avoid extended driving and have your vehicle inspected by a mechanic as soon as possible to prevent further damage.
Symptoms
Engine misfire, rough idle, lack of power
Common Causes
- Failed ignition coil A (Cylinder 1)
- Damaged coil connector or wiring
- Bad spark plug
- Faulty PCM coil driver
How to Fix
- 1 Replace ignition coil A
- 2 Repair damaged wiring or connector
- 3 Replace spark plug
- 4 Test PCM output signal
Technical Explanation
To set P0351, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. Misfire rate is counted per cylinder over rolling windows and compared against two thresholds: a catalyst-damaging rate (triggers flashing MIL) and an emissions-exceeding rate (triggers solid MIL). The PCM logs which cylinder is misfiring based on crankshaft position at the time of each detected event. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
This fault carries real mechanical risk. The root causes — including failed ignition coil a (cylinder 1) — can trigger a chain reaction of component failures if the vehicle continues to be driven. Have it towed or drive directly to a shop without delay.
Mechanic's Pro Tip
Module replacement should always be the last resort for P0351 after exhaustively verifying all power supply circuits, ground connections, and communication bus wiring. Use a wiring diagram to locate all fuses, relays, and ground points for the affected module, and measure voltage drop on each ground with the circuit loaded. A module "failure" is frequently a corroded ground eyelet or a weak battery causing brownout conditions — fix these first and you'll save hundreds of dollars on an unnecessary module replacement.
Ignition coil replacement: $100 - $250