Fault code P0387 – crankshaft position sensor “B” circuit low input

Fault code P0387 is called “Crankshaft Position (CKP) Sensor “B” Circuit Low Input” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0387

This diagnostic trouble code (DTC) is a generic code. Error P0387 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P0387 – crankshaft position sensor

Depending on the vehicle, the PCM uses the crankshaft position information to correctly determine spark timing. But in some systems, only for ignition timing detection and does not control ignition timing.

The CKP sensor is stationary and works in conjunction with a toothed ring attached to the crankshaft. When this ring passes in front of the CKP sensor, the magnetic field produced by the sensor is interrupted. This creates a voltage signal which the PCM interprets as the position of the crankshaft.

If the PCM detects no crankshaft pulses, or if it sees a problem with the pulses in the output circuit, code P0387 is set.

In other words, when the engine is running, the PCM continuously compares the input signals from the crankshaft and camshaft. If the crankshaft position is not within the specified degree of deviation from the camshaft position. At the specified set of programmed circumstances, within the specified time period. Code P0387 will be stored, and the malfunction indicator lamp may illuminate.

Quite often when this code is set, the engine will not start. If the engine does start, it is likely to run very badly.

Symptoms of vehicle malfunctions

The main signal that an error P0387 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will light up.
  2. The engine may run, but with reduced performance (loss of power).
  3. The engine may crank, but not start.
  4. The vehicle may stall or start poorly.
  5. Jerking/missing ignition at idle or under load.
  6. Increased fuel consumption.

Depending on the make and model, the engine control unit may use the CKP sensor to evaluate the engine speed and position. Therefore, the engine will run but not at maximum efficiency when P0387 is malfunctioning. In this case, you may experience difficulty starting up, sharp idling, or poor acceleration.

Factors that can cause this error code

The error code P0387 can mean that one or more of the following problems have occurred:

  • Defective CKP crankshaft position sensor.
  • CKP sensor connector is damaged.
  • Cogs are missing or the keyway of the timing belt is cut off.
  • Timing chain is stretched, or timing belt tooth has slipped due to wear
  • Alignment of timing belt/chain is faulty.
  • Timing belt has broken.
  • Timing belt / chain tensioner is damaged.
  • CMP solenoid valve is stuck in open position.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0387

Some suggested steps for troubleshooting and fix the error code P0387:

  1. Visually inspect the crankshaft and camshaft position sensor electrical leads and connectors.
  2. Check the level, condition, and viscosity of the engine oil.
  3. Read all stored data and error codes with an OBD-II scan tool. To determine when and under what circumstances the error occurred.
  4. Clear the error codes from the ECM memory and test drive the vehicle to see if code P0387 appears again.
  5. Inspect the drives, belts, or timing chains for wear.
  6. If the problem is not detected, continue diagnosing by following the procedure set by the vehicle manufacturer.

Follow the vehicle manufacturer’s recommendations when diagnosing and correcting this error. Failure to do so may result in serious engine damage, as well as hasty replacement of serviceable components.

Diagnose and repair of problems

Begin diagnostics by visually inspecting all system-related wiring harnesses and connectors. Inspect electrical circuits, sensors, and connectors that are contaminated with engine oil, coolant, or power steering fluid.

Petroleum-based fluids are known to corrode protective wire insulation and short or open circuits. This can cause the error P0387 to appear.

Test with a multimeter

Then connect the scan tool to the vehicle’s diagnostic port and retrieve all the stored fault codes. After that, continue testing the voltage and ground signals. Most models use a five volt power supply. Also check the ground signal, and the third wire, the control circuit, should supply a signal to the PCM.

Disconnect the electrical connector from the CKP sensor and test it following the manufacturer’s recommendations, using a multimeter. Replace the sensor if the resistance values do not meet the manufacturer’s specifications. If all CKP circuit resistance values are within specifications, go to next step.

Oscilloscope test

Connect the positive test lead of the oscilloscope to the signal wire of the CKP harness, and connect the negative lead to the CKP ground circuit. Select the appropriate voltage setting on the oscilloscope and turn it on.

With the transmission in park or neutral and the engine idling, observe the waveform on the oscilloscope. Focus on any unexpected spikes or glitches in the waveform pattern.

If you notice any spikes or glitches, gently wiggle the wiring harness and connector while looking at the waveform pattern. You are trying to determine if the problem is a weak connection or a faulty CKP.

Notice the voltage blocks in the waveform pattern. If some of them are missing, it indicates a broken or worn gear ring. Also check the CKP magnetic tip for excessive metal debris and clean if necessary. If the waveform is normal, go to the next step.

Now reconnect the oscilloscope test leads to the same circuits near the PCM connector and observe the waveform pattern. If you find a deviation, there is most likely an open or short between the CKP connector and the PCM connector.

If no open or shorted circuits are found, the problem with error P0387 may be a faulty PCM or its programming.

On which vehicles does this problem occur most frequently

Fault code P0387 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • BMW
  • Dodge (RAM)
  • Ford
  • Jeep
  • Nissan

Fault code P0387 can sometimes be found with other errors. The most common are the following: P0385, P0386, P0388, P0389.


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