What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (Jeep, Nissan, Dodge, Ram, BMW, Ford, GM, etc.). Although generic, the specific repair steps may vary by make/model.
When I have diagnosed a stored P0387 code (in the past), it’s because the Powertrain Control Module (PCM) detected a low voltage input signal from the secondary crankshaft position sensor (CKP) circuit. The B sensor typically refers to a secondary CKP sensor in a system that uses multiple CKP sensors.
CKP sensors are responsible for monitoring engine speed (RPM) and crankshaft position. These two factors are used in various engine management scenarios but are particularly important for ignition (spark) timing and fuel delivery.
The crankshaft position, especially relative to the camshafts, is one of the key factors used by the PCM to calculate ignition spark timing. Camshafts rotate at half the speed of the crankshaft, so it is important for the PCM to be able to distinguish between the engine’s intake and exhaust strokes (rotations). The CKP sensor and each camshaft position sensor (CMP) have at least one dedicated circuit to provide the PCM with an input signal, a 5-volt reference signal, and a ground.
CKP sensors are typically Hall effect electromagnetic types. They are mounted externally on the engine in very close proximity (usually only a few thousandths of an inch) to a circuit completing the engine ground. This engine ground is typically a reluctor ring (with precision-machined teeth) attached to one end of the crankshaft or integrated into the crankshaft itself.
The CKP sensor is mounted so that the crankshaft’s reluctor wheel passes very close to its magnetic tip. As the crankshaft rotates, the raised areas (on the reluctor wheel) complete an electromagnetic circuit with the sensor. When the gaps between the teeth pass the CKP sensor, the circuit is briefly interrupted. These circuit interruptions create voltage fluctuations that the PCM perceives as a waveform pattern.
With the engine running, the PCM constantly compares the input signals from the CKP and CMP sensors. If the CKP input signal voltage is lower than expected under certain circumstances, a P0387 code will be stored, and a MIL may be illuminated.
Other B Crankshaft Position Sensor malfunction codes include P0385, P0386, P0388, and P0389.
Code Severity and Symptoms
When a P0387 is stored, the engine will likely not run, and this code should be classified as severe. Even if the engine starts and runs, there is a high risk of a no-start condition, and there will be driving repercussions.
Symptoms of this code may include:
Engine does not start
Tachometer (if applicable) does not register RPM when the engine is cranked
Hesitation during acceleration
Poor engine performance
Reduced fuel economy
Causes
Possible causes for this code being set are:
Faulty CKP sensor
Open or shorted wiring to the CKP sensor
Corroded or fluid-soaked connector at the CKP sensor
PCM programming error or faulty PCM
Diagnostic and Repair Procedures
Before diagnosing a P0387 code, I need access to a suitable diagnostic scanner, with an integrated digital volt/ohmmeter (DVOM) and an oscilloscope. I will also need access to All Data DIY (as a reliable source for vehicle information).
A viable starting point for any code diagnosis is a visual inspection of the wiring harnesses and connectors related to the system. Since petroleum-based fluids compromise the protective insulation of wiring and lead to short or open circuits (and a stored P0387), circuits, electrical sensors, and/or connectors that have been contaminated by engine oil, coolant, or power steering fluid should be examined carefully.
If everything looks okay, connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes and freeze frame data. I like to note this information down as it can be helpful if the P0387 proves to be intermittent.
Test voltage at the CKP sensor in question. A five-volt reference is typically used for CKP sensor operation, but check the manufacturer’s specifications for the vehicle in question. There should also be a ground signal and one or more output circuits. If the reference voltage and ground circuits are detected at the CKP sensor connector, proceed to the next step.
After disconnecting the electrical connector from the CKP sensor in question, test it according to the manufacturer’s specifications using the DVOM. If the CKP sensor resistance levels do not meet the manufacturer’s specifications, replace it. If the CKP sensor matches the specifications, proceed to the next step. Reconnect the CKP sensor in question. Attach the oscilloscope’s positive test lead to the signal output wire and connect the negative lead to the sensor’s ground circuit. Now, power on the oscilloscope and select the appropriate voltage setting. With the engine running, observe the waveform on the oscilloscope, focusing on unexpected spikes or glitches. If spikes or glitches are observed, carefully wiggle the wiring harness and connector of the CKP sensor in question to determine if the issue is a loose connection or a faulty sensor. If missing voltage blocks are noticed in the waveform pattern, suspect a broken or worn reluctor ring or that the magnetic tip of the CKP sensor contains excessive metallic debris. If no issues are detected in the waveform, proceed to the next step.
Connect the oscilloscope test leads to the CKP sensor signal input and ground circuits near the PCM connector and observe the waveform pattern. If the waveform pattern near the PCM connector is different from what was seen when the test leads were connected near the CKP sensor, suspect an open or shorted circuit between the CKP sensor connector and the PCM connector. If this is the case, disconnect all associated controllers and begin testing individual circuits with the DVOM. Shorted or open circuits must be repaired or replaced. If the waveform pattern is identical to what was seen when the test leads were connected near the CKP sensor, suspect a faulty PCM or a PCM programming error.
Additional Diagnostic Notes:
Some manufacturers recommend replacing CKP and CMP sensors as a set
Use technical service bulletins to aid the diagnostic process