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P035AIgnition Coil "M" Primary/Secondary Circuit

The PCM has detected a fault in the primary or secondary circuit of ignition coil "M", which fires cylinder 13 on engines with thirteen or more cylinders.

Definition

The PCM drives each coil-on-plug ignition coil through a low-current primary control circuit and monitors it for the expected voltage feedback each time the coil is commanded to fire. P035A sets when the coil "M" (cylinder 13) primary circuit shows an open, short, or missing feedback signal, or when secondary-side breakdown is detected. Expect a dead or misfiring cylinder 13, a steady or flashing MIL, rough running, and reduced power; a sustained misfire can overheat and damage the catalytic converter. This code applies only to high-cylinder-count engines such as V16s.

Common causes

  • Failed ignition coil (open or shorted primary winding, or internal secondary arcing)
  • Damaged, corroded, or loose coil connector at cylinder 13
  • Chafed or open wiring in the coil control or supply circuit
  • Loss of battery voltage feed to the coil (blown fuse or ignition relay fault)
  • Poor engine or coil ground connection
  • Failed coil driver inside the PCM (least common)

Common misdiagnoses

  • Spark plugs replaced when the fault is in the coil control wiring
  • Fuel injector replaced for what is an ignition-side dead cylinder
  • PCM replaced before wiring and connector faults are ruled out
  • All coils replaced when only the cylinder 13 coil or its circuit is at fault

Troubleshooting steps

  1. 1.Swap the coil with an adjacent cylinder

    Move the cylinder 13 coil to a neighboring cylinder and clear the code; if the fault follows the coil (e.g., P035B sets instead), replace the coil.

  2. 2.Inspect the coil connector and boot

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

  3. 3.Verify battery voltage at the coil feed

    With the key on, confirm approximately 12 V or more on the coil supply terminal; a missing feed points to a fuse, relay, or harness open.

  4. 4.Measure coil primary resistance

    Most COP primaries read roughly 0.4-2.0 ohms; an open or near-zero reading confirms a failed coil (check the service data for the exact spec).

  5. 5.Test the PCM control signal

    With a scope or noid-style test light on the control circuit while cranking, confirm the PCM is switching the primary; a good command with no spark condemns the coil, no command points to wiring or the PCM driver.

  6. 6.Check the harness routing

    Trace the coil sub-harness for chafe points against brackets or the valve cover, especially where heat shielding is missing.

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