P0351 indicates that the powertrain control module (PCM) has detected an open circuit condition in the primary control side of ignition coil A, which typically corresponds to cylinder number one. This means the electrical path needed to energize the coil’s primary winding is interrupted, preventing proper spark generation. The fault may lie in the coil itself, the connecting wiring, or—rarely—the controlling output from the PCM.
The coil assembly has an internal open in the primary winding or the connector terminal is damaged, preventing current flow through the control circuit.
The control circuit wire or ground path may be broken, rubbed through, or shorted to voltage or ground between the PCM and the coil.
Terminal spread, moisture intrusion, or corrosion at the coil connector creates a high-resistance or open connection that interrupts the primary circuit.
A loose, corroded, or broken ground strap or eyelet prevents the primary circuit from completing its return path to the battery.
The output transistor inside the PCM that switches the coil primary current has failed, though this is statistically unlikely compared to component-level faults.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
While a failed PCM driver can theoretically set this code, it is an uncommon root cause. In the vast majority of cases, the fault is a bad ignition coil, damaged wiring, or a connector issue. Replacing the PCM should only be considered after the coil, harness, and grounds have been thoroughly tested and ruled out.
No. This code specifically monitors the electrical integrity of the coil’s primary control circuit. A worn spark plug can cause a misfire but will not trigger an open-circuit fault in the coil primary; it would typically set a P0301 misfire code instead.
Driving is not recommended. A persistent misfire from this fault can allow raw fuel to enter the exhaust system, overheating and permanently damaging the catalytic converter. Additionally, the vehicle may exhibit dangerous hesitation or stalling in traffic.
Not exactly. An 'open' circuit code means the PCM sees a break in the path and cannot complete the circuit to energize the coil primary. The coil may not be receiving the switched ground (or control voltage, depending on design) required to build a magnetic field.