LS Swap P0335/P0336 Crank Sensor Codes or No Start: Signal, Reluctor, Wiring, and HP Tuners Diagnosis

Confirm whether the controller sees engine speed before blaming the calibration

P0335 indicates a crankshaft-position sensor circuit or missing-signal problem, while P0336 indicates that the signal's range, performance, or pattern is implausible for the controller. Neither code proves the sensor itself is bad. On an LS swap, the cause may be battery voltage, starter speed, sensor power or ground, signal wiring, connector pin fit, shielding, a 24x/58x mismatch, an incorrect sensor, damaged reluctor, excessive air gap, wrong controller or operating system, or mechanical movement. Save the exact DTC status and freeze-frame before clearing anything.

Connect VCM Scanner, read all codes, and log battery voltage, engine speed, ignition state, and any supported crank/cam synchronization or error channels during a controlled crank. HP Tuners' current Scanner guidance recommends reading DTCs before scanning and adding the channels needed for the diagnostic task. If scanner RPM remains zero while the engine physically turns, prove the crank-signal path before changing fuel, spark, injector, security, idle, or airflow tables. Stop for starter smoke, hot cables, fuel leakage, repeated backfire, mechanical noise, or an engine that cranks abnormally fast or unevenly.

• Save codes, status, freeze-frame, a short cranking log, and the current calibration before disconnecting power
• Verify the engine rotates normally and has oil pressure, compression evidence, and correct mechanical timing before prolonged testing
• Do not probe a sensor signal with a test light or apply voltage to a controller pin
• Keep fuel disabled when the approved test requires extended cranking and follow starter duty-cycle limits

Identify the engine, reluctor pattern, sensor, harness, and controller as a matched system

Early Gen III LS combinations commonly use a 24x crank reluctor and rear-mounted crank sensor with the matching cam pattern; later Gen IV combinations commonly use 58x crank and 4x cam patterns. Color is a clue, not a sufficient identification method after replacement parts, repainting, adapters, or mixed engine assemblies. Record block and crank information, reluctor tooth count when verified, sensor part number, sensor connector keying, harness part number, ECM service number, operating system, cam sensor location and pattern, and every adapter or conversion box.

Chevrolet Performance controller-kit instructions show that the ECM, harness, sensors, power distribution, grounds, and engine package are engineered together. Holley's LS wiring documentation likewise separates 24x and 58x crank/cam requirements. A 24x sensor on a 58x wheel, wrong voltage family, swapped signal and reference wiring, or controller configured for another pattern can create a clean-looking installation that never produces usable rpm. Resolve component identity before continuity testing or replacement.

Test power, ground, signal integrity, air gap, reluctor condition, and cranking voltage

Use the exact controller and sensor diagram to backprobe safely. Verify sensor supply and ground under cranking load, not only with the key on. Inspect terminal tension, seals, bent pins, backed-out terminals, oil or coolant intrusion, harness strain, exhaust heat, bellhousing or header contact, splice quality, shield and drain treatment where specified, and shared grounds between battery, block, cylinder heads, chassis, ECM, and fuse/relay center. Voltage drop can corrupt the sensor and controller even when an unloaded meter shows battery voltage.

If the circuit and identities are correct, inspect sensor seating, O-ring or bracket interference, air gap, reluctor runout, bent or missing teeth, wheel installation direction, crank endplay, thrust movement, and damage from prior engine work. A lab scope is often the decisive tool: compare amplitude, spacing, missing-tooth signature, noise, and cam relationship while cranking. P0336 can follow a distorted waveform that still produces an RPM number. Avoid a crank relearn until the engine runs correctly and the service procedure actually calls for it; a relearn cannot repair a missing or physically incorrect signal.

Repair the signal path, then verify synchronization before calibration work

The correction may be battery and starter service, ground or power-distribution repair, terminal or harness repair, the correct sensor, proper sensor seating, a matched 24x/58x harness and controller strategy, reluctor repair, mechanical timing correction, or replacement of a damaged controller input after all external causes are proven. Clear codes only after preserving evidence, then repeat the same cranking log. Confirm credible and stable RPM, normal voltage, no returning crank or cam codes, correct synchronization data where supported, and spark and injector command before addressing fuel pressure, VATS, tune, or airflow.

Ironwake diagnoses LS-powered classic cars and trucks for owners in King George, Fredericksburg, Stafford, Spotsylvania, Dahlgren, Colonial Beach, the Northern Neck, and nearby Southern Maryland. Send the vehicle, engine and crank identification, reluctor and cam pattern, sensor and harness part numbers, ECM service number and operating system, wiring diagram, battery and cranking-voltage results, DTC report, VCM Scanner log, recent engine or harness work, and clear connector and routing photos. That record keeps a classic-car LS project focused on verified integration rather than late-model parts swapping by guesswork.