Engine

P0385 — Crankshaft Position Sensor B Circuit Malfunction

Severity: medium Drive with care, to a shop

What P0385 means

The engine control module uses the crankshaft position sensor signal to know engine speed and shaft position, which it needs for spark and fuel timing. P0385 sets when the sensor B signal is missing, erratic or out of range. Sensor B is usually a second or backup crank sensor circuit, but its exact location varies by manufacturer.

Symptoms

  • Check Engine light on
  • Hard starting or no-start
  • Rough idle or misfires
  • Engine stalling
  • Hesitation and loss of power
  • Tachometer needle jumping or dropping to zero

Possible causes

  1. Failed crankshaft position sensor B
  2. Damaged, chafed or corroded wiring and connector
  3. Sensor contaminated with metal debris or oil
  4. Damaged or misaligned reluctor (tone) ring
  5. Incorrect air gap or loose sensor mounting
  6. ECM fault (rare)

How to diagnose

  1. Scan for codes and freeze-frame data, and look for related codes such as P0335 or P0340
  2. Inspect the sensor, connector and harness for oil, chafing, corrosion or poor contact
  3. Check sensor mounting and air gap, and remove it to look for metal debris
  4. Test power, ground and signal wires with a multimeter following the factory wiring diagram
  5. Check sensor resistance (inductive type) or view the waveform with a scope while cranking
  6. Inspect the reluctor ring for missing teeth, cracks or dirt
  7. Watch RPM data on a scan tool while cranking
  8. If everything checks out, test the ECM and its power supply

Common fixes

  • Replace crankshaft position sensor B
  • Repair or replace damaged wiring and connectors
  • Replace or correctly reinstall the reluctor ring
  • Clean the sensor and mounting area and set the proper gap
  • Reflash or replace the ECM if confirmed faulty

Questions and answers

What does P0385 mean?

The ECM is not getting a valid signal from crankshaft position sensor B. Without it, the ECM can lose track of shaft position and upset spark and fuel timing.

Can I drive with P0385?

Only briefly and carefully. The engine can stall at any moment and may not restart, so fix the cause as soon as you can.

What most often causes P0385?

Most often it is the sensor itself or damaged wiring and connectors. A bad tone ring or ECM is less common, so start with inspection and circuit tests.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.