What Does P0387 Mean?
The crankshaft position sensor B circuit is reporting a low input signal to the ECM. This means the voltage from sensor B is below the minimum threshold the ECM expects. On a magnetic (variable reluctance) sensor this could mean the signal amplitude is too weak; on a Hall-effect sensor it means the signal is stuck near ground. The engine may exhibit misfires, rough running, or stalling, especially at low RPM where magnetic sensor output is naturally weakest.
Safety Warning
A low CKP signal can cause engine stalling, particularly at low RPM such as idle or during deceleration. This can result in loss of power steering and brake assist. The vehicle should be repaired before extended driving. If driving is necessary, avoid low-speed situations where stalling is most likely.
Common Causes
30%
CKP sensor B signal wire shorted to ground through damaged insulation
25%
Failed CKP sensor B with internally shorted windings (low resistance output)
20%
Excessive sensor air gap causing the magnetic sensor output to be below the ECM detection threshold
15%
Corroded connector or high-resistance ground return reducing signal amplitude
10%
Damaged reluctor ring with eroded teeth reducing magnetic flux change
Diagnostic Steps
1
Measure CKP sensor B output voltage with an oscilloscope while cranking. For a magnetic sensor, the output should be >0.3V AC at cranking speed. For a Hall-effect sensor, verify the signal switches between near-0V and near-5V.
2
Disconnect the CKP sensor B and measure resistance between the signal and return pins. Compare to specification (typically 500-1500 ohms for magnetic sensors). A reading significantly below spec indicates shorted windings.
3
With the sensor disconnected, check for shorts to ground on both signal wires at the harness connector. Either wire reading near 0 ohms to ground confirms a wiring short.
4
Inspect the sensor air gap and verify it meets specification. On some applications, the sensor uses a paper spacer on the tip that sets the gap on initial installation — if the sensor was removed and reinstalled, the gap may be incorrect.
5
Verify the 5V reference voltage and ground (for Hall-effect sensors) or the sensor ground return (for magnetic sensors) are intact at the harness connector. A missing ground will result in a low or absent signal.
Estimated Repair Cost
$80 - $400
Parts + labor, varies by vehicle and location
The crankshaft position sensor B circuit is reporting a low input signal to the ECM. This means the voltage from sensor B is below the minimum threshold the ECM expects. On a magnetic (variable reluctance) sensor this could mean the signal amplitude is too weak; on a Hall-effect sensor it means the ...
The most common cause of P0387 (Crankshaft Position Sensor B Circuit Range/Performance) is: CKP sensor B signal wire shorted to ground through damaged insulation
Typical repair costs for P0387 range from $80 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A low CKP signal can cause engine stalling, particularly at low RPM such as idle or during deceleration. This can result in loss of power steering and brake assist. The vehicle should be repaired before extended driving. If driving is necessary, avoid low-speed situations where stalling is most likely.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0387 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition / Engine Timing System
Difficulty
Type
Generic (SAE)
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