P0387 Code: Crankshaft Position Sensor B Circuit Low

What the P0387 code means

Some engines carry a second crankshaft sensor for redundancy or for a more precise reading. If it fails, the computer falls back on sensor A or on the camshaft signals.

Position sensors come in two types. An inductive sensor has two wires and makes its own alternating voltage. A Hall effect sensor has three wires: a supply, a ground and a square wave signal between 0 and 5 volts. The computer watches for the presence of the signal, for its shape and for how it lines up with the other position signals.

A low signal normally means the signal wire is shorted to ground, or the sensor is not getting its supply. That is what sets the P0387 code.

Keep in mind that the code tells you where the computer saw the fault, not necessarily which part is bad. Check the connector, the wiring and the supply before you buy a sensor.

P0387 code symptoms

• Long cranking, or the engine does not start.
• Stumbling or cutting out while driving.
• Engine that stalls, especially when hot.
• Loss of power, with variable valve timing disabled.
• Check engine light on, sometimes with misfire codes.

Likely causes of the P0387 code

1. Connector with oil, corrosion or a loose fit. This is the most frequent cause on camshaft sensors.
2. Wiring damaged by heat or by rubbing, especially near the exhaust. A signal wire rubbed through to ground gives a low reading.
3. Failed sensor. An internal fault, often when it heats up.
4. Damaged tone wheel or reluctor ring. Teeth that are broken or dirty.
5. Timing out of phase or a stretched chain.
6. Missing supply reference. 5 volts or 12 volts, depending on the design.

How to diagnose the P0387 code step by step

1. Watch rpm and the sync status on the scan tool while someone cranks the engine.
2. Inspect the connector. Look for oil inside, green pins or a broken lock.
3. Check supply and ground on three-wire sensors: 5 or 12 volts, with less than 0.1 volt of drop on the ground. A missing supply is a prime suspect for a low signal.
4. Measure the signal with a scope or a multimeter in frequency mode while cranking. On inductive sensors, read the alternating voltage.
5. Look at the tip of the sensor. Metal shavings stuck to it or impact marks matter.
6. Test the signal wire for a short to ground with the connector unplugged.

How to fix the P0387 code

• Clean or repair the connector and the wiring.
• Replace the sensor with an original-quality part.
• Repair the tone wheel or the timing if it is damaged.
• Run the crankshaft variation learn procedure if the manufacturer requires it.
• Clear the codes and verify the repair.

Technical reference data

• Inductive sensor: two wires, resistance of 200 to 1,200 ohms.
• Hall effect sensor: three wires, square wave signal from 0 to 5 volts.
• Typical air gap: 0.5 to 1.5 mm (about 0.020 to 0.060 inch).
• These are approximate values, so check the manufacturer data for your engine.

Brand-specific notes

Heat is a common reason these sensors act up. A sensor that fails only when hot will stall the engine, then let it restart once it cools down.

P0387 on Chrysler

On many Chrysler engines the camshaft and crankshaft sensors fail with temperature: the engine stalls when hot and starts again after it cools.

P0387 on Nissan

On many Nissan engines the camshaft and crankshaft sensors fail with temperature: the engine stalls when hot and starts again after it cools.

P0387 on Hyundai

On many Hyundai engines the camshaft and crankshaft sensors fail with temperature: the engine stalls when hot and starts again after it cools.

P0387 on GM

After you replace the CKP sensor on a GM vehicle, you often have to run the crankshaft variation learn procedure with a scan tool.

P0387 on Ford

After you replace the CKP sensor on a Ford vehicle, you often have to run the crankshaft variation learn procedure with a scan tool.

Frequently asked questions about P0387