LS Swap P0351–P0358 Ignition Coil Circuit Codes or No Spark: Power, Grounds, Harness, ECM, and HP Tuners Diagnosis

Sort one-cylinder, one-bank, and all-coil failures before buying parts

P0351 through P0358 identify ignition-coil primary or secondary circuit faults by cylinder, but a code does not prove the coil itself failed. Record every current, pending, and history code plus freeze-frame data before clearing anything. Note whether the engine cranks, starts briefly, misfires only under load, loses one bank, or has no spark anywhere. Stop cranking if coils, drivers, grounds, connectors, or harnesses overheat; repeated operation into a short can damage the ECM and catalytic converters.

Identify the engine, crank and cam reluctor families, ECM and calibration, coil part numbers, harness supplier, fuse and relay layout, grounding scheme, spark-plug and wire types, and every extension or repair. Confirm the firing order and connector bank labels rather than trusting wire color. Holley's LS harness instructions distinguish the odd and even coil connectors and call out separate coil grounds; crossing bank connectors or leaving a ground floating can create multiple cylinder faults that imitate an ECM problem.

• Disable fuel and follow the ignition-system service procedure before checking spark
• Use an approved spark tester; do not hold a plug, wire, or coil output by hand
• Do not probe ECM or coil terminals with a test method that can spread terminals or overload a driver
• Preserve the original DTC, freeze-frame, crank-speed, sync, voltage, and misfire evidence before clearing codes

Verify cranking voltage, coil power, and every required ground under load

Begin with battery state, cranking voltage, engine-to-battery grounds, ECM grounds, ignition feed, coil fuses, relays, and voltage drop while the fault is present. Key-on voltage at an unloaded connector is not proof that the circuit can support coils during cranking. Back-probe using approved terminals and compare the failed cylinder or bank with a known-good branch. A common feed problem can disable several coils; a local splice, connector, or ground fault may affect only one side.

Inspect cylinder-head ground points, ring terminals, paint, powder coat, corrosion, loose fasteners, undersized straps, and grounds moved during exhaust or accessory work. Chevrolet Performance controller instructions specify battery, ignition, and ground connections for the supplied harness because the ECM, coils, injectors, and sensors depend on a stable reference. Confirm the ignition circuit remains powered in both RUN and START; an old switch or incorrectly separated accessory circuit can remove coil power only while the starter is engaged.

Use HP Tuners data and safe circuit tests to separate input, command, and coil faults

In VCM Scanner, log battery voltage, engine speed during cranking, cam and crank synchronization where supported, commanded fuel state, misfire counters, and the relevant diagnostic status. If engine speed or sync is missing, resolve the crank and cam input path before condemning eight coil circuits. If the ECM sees correct position data and one cylinder sets a repeatable circuit code, compare coil power, ground, connector drag, control-wire continuity, and behavior with a known-good coil moved according to the service procedure.

Check the control circuit for open, short-to-ground, short-to-voltage, cross-connection, exhaust damage, sharp-edge abrasion, water intrusion, poor crimps, incorrect pinning, and terminal tension. Do not substitute a conventional incandescent test lamp on an ECM driver. An oscilloscope and current-limited test equipment can show whether the ECM is commanding the coil and whether the primary circuit responds, but interpretation must match the exact ECM and coil design. A calibration cannot repair missing power, an open ground, reversed pins, or a shorted harness.

Repair the circuit, protect the harness, and validate under heat and load

The repair may involve coil, connector or sub-harness replacement; splice repair with sealed automotive methods; correct fuse, relay, and RUN-CRANK feed; restored cylinder-head and ECM grounds; revised routing and heat shielding; correct odd and even bank connections; or ECM repair after every external cause is eliminated. Use the correct coil family and dwell strategy for the hardware. Do not lengthen, repin, or relocate circuits casually around headers and fabricated mounts where vibration, heat, and ground paths differ from the donor vehicle.

After repair, verify clean cold and hot starts, stable cranking voltage, no current or pending P035x codes, correct cylinder order, normal coil and harness temperature, stable misfire counters, and repeatable operation under controlled road load. Save the before-and-after scan and document every wiring change. Ironwake diagnoses LS-powered classic-car builds for owners in King George, Fredericksburg, Stafford, Spotsylvania, Dahlgren, Colonial Beach, the Northern Neck, and nearby Southern Maryland. Send the engine, ECM, operating system, harness and coil details, DTC list, tune file, scan log, wiring diagram, fuse and relay layout, ground photos, and failure conditions before transport.