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P0351Ignition Coil "A" Primary/Secondary Circuit Malfunction

An electrical fault has been detected in the primary or secondary circuit of ignition coil "A", which serves cylinder 1.

Definition

The PCM switches ignition coil A's primary winding to ground to fire cylinder 1 and monitors the circuit for correct current rise and switching feedback; P0351 sets when it detects an open, short, or absent feedback on that specific circuit. The usual result is a persistent or intermittent cylinder 1 misfire — rough idle, hesitation, fuel smell, and often a companion P0301 — with a MIL that may flash under load. Continued driving with the dead cylinder sends unburned fuel into the exhaust and can overheat the catalytic converter, so the coil circuit should be repaired promptly.

Common causes

  • Failed cylinder 1 ignition coil (open or shorted primary winding)
  • Damaged wiring or chafed insulation in the coil A control or feed circuit
  • Corroded, loose, or oil/water-contaminated coil connector
  • Open ignition feed to that coil (broken wire or shared-fuse issue)
  • Carbon-tracked coil boot or plug well flashing over (secondary fault)
  • PCM coil driver failure (rare)

Common misdiagnoses

  • Replacing all ignition coils when only the cylinder 1 circuit is faulty
  • Replacing the injector for the cylinder 1 misfire
  • Replacing the PCM without testing the trigger circuit
  • Repeatedly replacing the coil when chafed wiring keeps killing the circuit

Troubleshooting steps

  1. 1.Swap the cylinder 1 coil with another cylinder

    If the code or misfire follows the coil (P0351 becomes P0352, etc.), replace the coil; if it stays on cylinder 1, the fault is in the wiring, connector, or PCM driver.

  2. 2.Verify power at the coil connector

    Confirm battery voltage on the feed wire key-on; check the fuse and any splice shared with other coils if it is missing.

  3. 3.Test the trigger signal

    Scope the control wire while cranking and confirm a clean switching pattern from the PCM; a missing trigger with good wiring continuity points to the PCM driver.

  4. 4.Measure coil primary resistance

    Compare to spec (typically 0.4-2 Ω across the primary terminals) and reject the coil on an open or shorted reading.

  5. 5.Inspect the connector, boot, and plug well

    Look for spread terminals, corrosion, oil in the plug well from a leaking valve cover gasket, and carbon tracking on the boot and plug insulator.

  6. 6.Clear codes and road test

    Confirm zero cylinder 1 misfire counts under load and no code reset over a complete drive cycle.

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