Fix P0387: STEP-BY-STEP diagnostic GUIDE!

The P0387: Crankshaft Position Sensor B Circuit Low Input code indicates that the engine control module (ECM) is detecting a lower-than-expected signal from the crankshaft position sensor B circuit. The crankshaft position sensor provides critical data on the crankshaft’s position and speed to manage engine timing and fuel injection. A low input signal can lead to performance issues such as misfires or stalling.

P0387 – Quick Overview

Meaning	P0387: Crankshaft Position Sensor B Circuit Low Input
Is it serious?	Yes, this code can lead to engine misfires, poor performance, stalling, or prevent the engine from starting.
Possible causes	– Faulty crankshaft position sensor – Low voltage supply – Wiring or connector issues
How to diagnose?	– Test the crankshaft position sensor for low input – Check the sensor power supply voltage – Inspect wiring and connectors for faults

P0387 Meaning

The P0387: Crankshaft Position Sensor B Circuit Low Input code means that the ECM is receiving a lower-than-expected signal from crankshaft position sensor B. This sensor provides important information for proper engine timing. A low signal can be caused by sensor failure, poor power supply, or wiring problems, and it may cause engine misfires, rough idling, or even prevent the engine from starting.

Step-by-step diagnostic guide

Follow these steps to diagnose and resolve the P0387 code by addressing potential causes one by one.

Action	Description	Tools Needed
Check for Other Codes	Use an OBD-II scanner to check for additional related codes that could provide more information about the crankshaft position sensor or other related systems.	OBD-II Scanner
Test the Crankshaft Position Sensor for Low Input	Use a multimeter to test the signal output from crankshaft position sensor B. Compare the signal with manufacturer’s specifications to determine if the sensor is functioning correctly.	Multimeter, Manufacturer’s Specifications
Check the Sensor Power Supply Voltage	Verify that the crankshaft position sensor is receiving the correct voltage from the power supply. Low voltage can lead to insufficient signal output. Ensure that the power supply is within the expected range.	Multimeter, Manufacturer’s Specifications
Inspect Wiring and Connectors for Faults	Inspect the wiring and connectors for the crankshaft position sensor B for signs of damage, corrosion, or loose connections that could cause a drop in signal. Repair or replace any faulty wiring or connectors as needed.	Flashlight, Wiring Repair Kit
Replace Faulty Components	If the crankshaft position sensor or wiring is faulty, replace the necessary components to restore proper signal output and engine timing.	Replacement Crankshaft Position Sensor, Wiring Components
Clear the Code and Test Drive	After completing repairs, clear the P0387 code using an OBD-II scanner. Test drive the vehicle to ensure the problem is resolved and the engine runs smoothly.	OBD-II Scanner, Vehicle Owner’s Manual
Recheck for Codes	After the test drive, re-scan the vehicle to confirm that the P0387 code has not returned. If the code reappears, further diagnosis may be required.	OBD-II Scanner

This diagnostic guide will help you resolve the P0387 code, ensuring that crankshaft position sensor B and its circuit are functioning correctly, allowing the ECM to maintain accurate engine timing and performance.