P0387 Code Meaning and Next Steps

First checks take 10 minutes for basic checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The vehicle suddenly runs much worse, loses power sharply, or the check-engine light starts flashing.
!There is a strong smell, smoke, overheating, or any symptom that suggests a real-time safety problem rather than a stored code alone.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored if drivability changes are obvious.

What to check first

Step-by-step checks

1
Free - no tools
Check whether the engine has a hard-start, stall, or no-start symptom with the code
2
Free - no tools
Inspect the sensor connector and harness for oil, heat, or abrasion damage
3
Basic tool needed
Look for related crankshaft, camshaft, or misfire codes that may help with diagnosis
4
Basic tool needed
If scan data is available, confirm whether the signal is truly missing or just too weak
5
Basic tool needed
Notice whether the code appeared after timing work or sensor replacement

If the code returns

-If no signal is present at the sensor, wiring or sensor failure becomes more likely.
-If the sensor tests okay, inspect the tone wheel and mechanical side of the engine.
-If the code returns after repair, recheck sensor fit and connector condition.

Background

What this code means

P0387 is a generic OBD-II code for a low or missing crankshaft position sensor B signal.

If the engine controller cannot see enough signal from the sensor, the issue is often the sensor itself, an open circuit, or a damaged reference wheel.

Diagnosis

Common causes

Most common

Failed crankshaft position sensor B

The sensor may no longer produce a usable signal.

Common

Open circuit or broken wire

A break in the circuit can remove the signal entirely.

Common

Damaged tone wheel

The reference source may no longer be readable.

Possible

Connector damage

A loose or corroded connector can behave like an open circuit.

Avoid these mistakes

What not to do

xDo not replace the ECU first if the sensor or tone wheel is visibly damaged.
xDo not keep cranking a no-start engine without checking the crank signal path.

Parts

Parts that may need replacing

PartTypical costNotes

Crankshaft position sensor B$40-$180Worth checking when the signal is missing or too low.

Connector or wiring repair$50-$250Useful when the circuit is open or intermittently open.

Tone wheel or reluctor repair$200-$900Relevant when the mechanical reference pattern is missing or damaged.

Related OBD codes

P0385

P0385 means the crankshaft position sensor B circuit has a malfunction.

P0386

P0386 means the crankshaft position sensor B signal is out of range or not believable.

P0388

P0388 means the crankshaft position sensor B signal is too high.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0387 was seeded from dtcdb and then expanded around crankshaft position sensor B low-input faults, with emphasis on sensor, wiring, and tone-wheel checks.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0387 - The Crankshaft Position Sensor B Signal Is Too Low or Missing