P0385

Universal

Crankshaft Position Sensor B Circuit Malfunction

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The engine computer monitors the crankshaft position sensor B circuit for a usable signal. Crankshaft position and speed information helps it coordinate engine operation. A circuit malfunction can cause starting or running problems, but the code alone does not prove the sensor needs replacement; wiring, connections, or other parts of the signal system may be involved.

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⚠️ Before You Begin (Safety First)

If the engine stalls, runs very roughly, or is difficult to keep running, avoid driving because it may stop unexpectedly. Arrange diagnosis or towing if it cannot be operated reliably. Exact checks depend on the vehicle, year, and engine.

Common Symptoms

  • The engine may crank longer than usual or fail to start if the computer cannot get a usable crankshaft signal.
  • The engine may stall or run roughly if the signal becomes intermittent while running.
  • Engine performance may be inconsistent because crankshaft position and speed information supports engine control.
  • There may be no noticeable symptoms if the fault is intermittent or does not disrupt engine operation.

Common Causes

  • A fault within crankshaft position sensor B may interrupt or distort its signal.
  • Damaged, loose, corroded, or poorly connected wiring or connectors may disrupt the circuit.
  • A problem with circuit power or ground, where applicable, may prevent a usable sensor signal.
  • Damage or a signal problem at the associated trigger wheel or other signal-generating components may affect the reading.
  • A fault in the engine computer or its input circuitry is possible but should be considered only after checking the circuit and signal sources.

Diagnostic Steps

  1. Note whether the engine has starting, stalling, or rough-running symptoms, and avoid driving if it cannot run reliably.
  2. Check for other diagnostic codes and record them before clearing anything; related codes can help narrow the cause.
  3. With the vehicle safely parked and the ignition off, visually inspect accessible sensor wiring and connectors for looseness, damage, corrosion, or contact with hot or moving parts.
  4. Do not unplug or probe components unless the vehicle-specific service information explains how to do so safely; avoid disturbing wiring if access requires unsafe work.
  5. If the visible checks do not reveal a clear issue, arrange vehicle-specific electrical and signal testing rather than replacing the sensor based only on this code.

When to Call a Professional

Check for related codes and compare crankshaft signal data with engine behavior. Use the vehicle-specific wiring diagram to test the sensor circuit, connector, power and ground where applicable, and signal. If basic circuit checks do not explain the fault, a technician can examine the signal with an oscilloscope and inspect the associated trigger wheel. Confirm the cause before replacing parts.

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Commonly Asked Questions

Does P0385 prove that crankshaft position sensor B has failed?

No. It identifies a malfunction in the sensor B circuit. The sensor, wiring, connectors, power or ground where applicable, and associated signal-generating components may need to be checked.

Can a vehicle with P0385 still run?

Possibly. Some vehicles may show few symptoms, while others may have trouble starting, run roughly, or stall. Do not continue driving if the engine cannot run reliably.

What does sensor B mean on my vehicle?

The designation and system layout can vary by vehicle. Use service information for the exact year and engine to identify the applicable sensor and circuit.

What tests can distinguish a sensor fault from a wiring fault?

A technician can inspect the connector and wiring, test the circuit using the vehicle-specific diagram, and examine the sensor signal during cranking or running as appropriate. The exact procedure varies by vehicle.

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