P0338 — Crankshaft Position Sensor A Circuit High

Causes

• Open or shorted wiring (short to battery/ignition voltage)
• Corroded, loose or damaged sensor connector or pins
• Failed crankshaft position (CKP) sensor (Hall or VR type)
• Short to an accessory power feed or ignition-switched supply
• Damaged or missing/cracked tone wheel (reluctor) or sensor air gap problem
• PCM/ECU internal fault or poor ground at PCM

Symptoms

• Check Engine Light (MIL) illuminated
• Hard or no-crank start, intermittent starting
• Engine stalls or runs roughly, misfires
• No or irregular tachometer signal
• Reduced engine power or limp mode depending on vehicle

What to check

• Read freeze-frame and live data for CKP signal and related codes (CMP correlation codes).
• Visual inspection of CKP sensor, connector, tone wheel/reluctor and wiring harness for damage or contamination.
• Wiggle test the harness and connector while monitoring live data to reproduce the fault.
• Measure reference supply and ground at the sensor with key ON (engine off).
• Probe signal at sensor and at the PCM pin to check for continuity and compare voltages.
• Use an oscilloscope to verify proper waveform shape, amplitude and timing while cranking/running.

Signal parameters

• Hall-effect (3-wire) CKP: reference typically ~5 V supply, signal is 0–5 V digital square wave. 'High' considered near supply (≈4–5 V), 'Low' near 0 V.
• VR (variable-reluctance, 2-wire) CKP: AC sine/alternating waveform. Amplitude varies with engine speed — small mV at cranking, rising with RPM. No DC reference present.
• Typical diagnostic thresholds: for Hall sensors a persistent signal voltage above expected active level (stuck high) will set a 'circuit high' fault; for VR sensors an unexpected DC offset or very high voltage may indicate short to supply.
• Actual resistance, voltages and waveform characteristics vary by vehicle — consult OEM electrical specifications before declaring out-of-range values.

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