P0338
Crankshaft Position Sensor A Circuit High InputP0338 is a generic OBD-II powertrain diagnostic trouble code: Crankshaft Position Sensor A Circuit High Input. It is logged by the engine control unit when the ckp/cmp monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0338 means
P0338 is set when the PCM detects that the signal voltage from Crankshaft Position Sensor "A" is persistently above the acceptable upper threshold. Under normal operation the CKP signal oscillates between a low reference and a high reference as reluctor teeth pass the sensor; a voltage that is stuck near battery or supply voltage indicates the output line has been pulled high rather than allowed to switch.
The most common root cause on Hall-effect sensors is a direct short between the sensor signal wire and the vehicle's 5 V reference supply or the 12 V power rail — whether caused by insulation breakdown, a pinched harness, or internal sensor failure that bridges the output to supply internally. On variable-reluctance sensors, an open return (ground) circuit can raise the apparent differential signal voltage above threshold. Corroded connector pins that bridge the signal and reference terminals are another frequent culprit. Like P0337, a persistent P0338 will prevent the PCM from determining crankshaft position, resulting in a no-start or severe misfires, since injection and ignition timing become undefined. Intermittent high readings typically cause stalling, rough idle, and erratic tachometer behavior.
Common causes
Most-frequently reported root causes when P0338 is logged.
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1
Harness short to the 5 V reference or 12 V supply rail forcing the signal wire to a high-fixed voltage
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2
Internal sensor failure bridging the signal output to the supply terminal
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3
Open ground return circuit on a variable-reluctance sensor raising the differential signal above threshold
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4
Corroded or contaminated connector bridging signal and reference pins
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5
Damaged reluctor ring (cracked, wobbling, or severely rusted) generating anomalous high-voltage spikes
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6
Broken timing belt or chain causing the reluctor to stop moving while the supply voltage remains applied
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7
Failed PCM input stage that misreads normal sensor output as high
Symptoms drivers notice
How to diagnose P0338
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and check live CKP sensor data while cranking — if RPM reads unrealistically high or the PID is pegged, the circuit is likely shorted high
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2
Inspect the sensor harness for contact with hot exhaust components or areas where insulation could rub through and short to the 5 V reference or battery positive
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3
Unplug the sensor and measure voltage on the signal wire relative to chassis ground with the ignition on — any significant voltage with the sensor disconnected confirms a harness short
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4
Check reluctor wheel condition through the sensor aperture for cracking, wobble, or heavy corrosion that could cause spurious high pulses
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5
Verify timing belt or chain integrity if the vehicle allows visual inspection; a snapped belt stops the reluctor while sensor supply remains live
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6
Test sensor resistance (VR type) or perform a bench voltage-output test (Hall type) to isolate internal sensor failure
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7
Repair any shorted wiring, replace the sensor if internal failure is confirmed, and clear codes before retesting
Related powertrain codes
- P000A — A Camshaft Position Slow Response Bank 1
- P000B — B Camshaft Position Slow Response Bank 1
- P000C — A Camshaft Position Slow Response Bank 2
- P000D — B Camshaft Position Slow Response Bank 2
- P0010 — A Camshaft Position Actuator Circuit (Bank 1)
- P0011 — A Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
Frequently asked questions
What is the difference between P0337 and P0338?
P0337 means the CKP signal is stuck or consistently low (below threshold), indicating an open circuit or short to ground. P0338 means the signal is stuck or consistently high (above threshold), typically pointing to a short to the reference voltage or supply rail.
Can a broken timing belt cause P0338?
Yes. If the timing belt snaps, the crankshaft still turns but the reluctor wheel may produce no pulses, and with the sensor supply voltage still applied and no switching occurring, the PCM can interpret this as a high-fixed signal and set P0338 alongside a no-start condition.
My car won't start and I have P0338 — is the sensor definitely bad?
Not necessarily. Check the wiring first: unplug the sensor and see if voltage is present on the signal wire. If it is, you have a harness short rather than a failed sensor. Only replace the sensor after ruling out wiring issues.
How serious is P0338?
Very serious. Without a valid crankshaft position signal the PCM cannot accurately time fuel injection or ignition, typically causing a no-start or severe misfire. The vehicle should not be driven until the fault is diagnosed and repaired.
Disabling P0338 in software
RaceTune can permanently disable P0338 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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