AutoFaultCodes.com
OBD-II fault code definitions, symptoms, causes, and step-by-step diagnostics.
Standardized generic DTCIgnition & misfire

P0387 — Crankshaft Position Sensor B Circuit Low

P0387 is the standardized powertrain DTC for “Crankshaft Position Sensor B Circuit Low.” The code identifies the monitored condition; it does not by itself prove which part failed.

Standardized generic definition
Crankshaft Position Sensor B Circuit Low
DTC category
Ignition & misfire
Diagnostic priority
Moderate to high because loss of crank/cam speed/position information can cause stalling or a no-start.
Copy code

What P0387 means

P0387 is the standardized powertrain DTC for “Crankshaft Position Sensor B Circuit Low.” The code identifies the monitored condition; it does not by itself prove which part failed.

Start with the stored data and the simplest external checks before replacing the component named in the code.

How to interpret the code wording

“Circuit Low” means the module saw voltage or a signal below its calibrated range. Depending on circuit design, likely test paths include a short to ground, missing reference/supply voltage, excessive resistance, poor terminal contact, or a failed sensor/actuator. Verify the circuit diagram and measure the circuit before replacing the named component.

Possible symptoms

  • Hard start or no-start
  • Stalling
  • Tachometer drop-out
  • Misfire or poor performance
  • Check Engine Light

Causes to test

These are diagnostic possibilities, not a statistical parts-replacement ranking. Vehicle-specific service information takes priority.

  • Sensor failure or incorrect air gap
  • Damaged reluctor/tone wheel
  • Open/short, poor connector fit, or shield/ground issue
  • Timing correlation problem
  • Low cranking voltage or control-module issue

Step-by-step diagnostic workflow

  1. Record whether the code sets during crank, startup, or while running.
  2. Check engine RPM and sync status during crank.
  3. Inspect sensor wiring and connector routing near hot/moving components.
  4. Use a scope when required to compare crank/cam waveform quality and correlation.
  5. Inspect reluctor/tone wheel and mechanical timing if electrical tests pass.
  6. Clear codes only after repair, then complete an appropriate drive cycle and verify the code and symptoms do not return.
Preserve evidence: EPA OBD guidance emphasizes that stored DTCs and freeze-frame data are important to proper diagnosis. Save them before clearing codes.

Scan data worth checking

  • Engine RPM during crank
  • Cam/crank sync status
  • Battery voltage during crank
  • Cam/crank position PIDs where available

Severity and drivability

Moderate to high because loss of crank/cam speed/position information can cause stalling or a no-start.

Stop driving and investigate immediately if there is a flashing MIL, oil-pressure warning, overheating, fuel leakage, severe misfire, major loss of power, abnormal mechanical noise, or a transmission that is slipping badly.

Common diagnostic mistakes

  • Replacing a sensor without inspecting the reluctor wheel
  • Ignoring weak battery/cranking voltage
  • Using resistance alone to judge an active Hall-effect sensor

Related generic codes

P0386 — Crankshaft Position Sensor B Circuit Range/PerformanceP0388 — Crankshaft Position Sensor B Circuit HighP0385 — Crankshaft Position Sensor B CircuitP0389 — Crankshaft Position Sensor B Circuit IntermittentP0390 — Camshaft Position Sensor B Circuit — Bank 2P0391 — Camshaft Position Sensor B Circuit Range/Performance — Bank 2

Source and accuracy notes

Generic DTC structure and standardized definitions are governed by SAE J2012/J2012DA. Actual enable criteria, thresholds, circuit pinouts, test values, software conditions, and repair procedures vary by vehicle. Use current OEM service information for the exact year/engine/calibration and check applicable manufacturer technical service bulletins. See the site methodology and primary-reference policy.