Faulty cylinder position sensor B (internal failure, no output); Damaged, chafed or open-circuit wiring between the sensor and the control unit (signal, supply or earth); Corroded, loose or contaminated sensor connector or pins; Incorrect sensor fitment, air gap or mounting issue after previous work; Damaged or mis-timed trigger wheel or reluctor, or timing drive fault (depends on engine); Low or unstable supply voltage from a weak battery or poor charging; Fault inside the engine control unit.

P1387

CYP Sensor B No Signal.

Infiniti
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
3: AreaIgnition system or misfire
87: FaultThe specific fault in that area

What it means

P1387 on an Infiniti is listed as 'CYP Sensor B No Signal'. CYP normally refers to the cylinder position (cam-related) sensor, and 'B' is a second sensor or circuit. The engine control unit saw no signal from that sensor while the engine was cranking or running, so it could not use it to confirm engine position. Which sensor is 'B' depends on the model and engine, so confirm this against the manufacturer's data for the vehicle.

Symptoms

Engine management light on
Long cranking or hard starting
Engine cranks but will not start
Rough running or misfire
Reduced power or the engine running in a limp-type mode
Stalling or intermittent cutting out

Possible causes

Faulty cylinder position sensor B (internal failure, no output)likely
Damaged, chafed or open-circuit wiring between the sensor and the control unit (signal, supply or earth)likely
Corroded, loose or contaminated sensor connector or pinslikely
Incorrect sensor fitment, air gap or mounting issue after previous workpossible
Damaged or mis-timed trigger wheel or reluctor, or timing drive fault (depends on engine)possible
Low or unstable supply voltage from a weak battery or poor chargingpossible
Fault inside the engine control unitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, and note any related crankshaft or camshaft position codes.
Check battery condition and charging voltage, as low voltage can upset sensor signals during cranking.
Visually inspect the sensor, its wiring and connector for chafing, oil contamination, heat damage, corrosion and a secure fit.
Locate sensor B for the specific model and engine using manufacturer data, and confirm its supply, earth and signal wiring layout.
With the ignition on, check the sensor supply voltage and earth at the connector, then test the signal wiring for continuity and shorts.
Watch the sensor signal live while cranking, using a scan tool or oscilloscope, and compare it with the crankshaft and other cam signals.
Inspect the sensor tip, mounting and trigger wheel for damage, debris or incorrect air gap.
Clear the code and road test to see whether it returns, checking whether it is intermittent with movement or heat.

How to fix

Replace the cylinder position sensor B if it is faulty or gives no signal.
Repair or replace damaged wiring, and clean or renew corroded connector terminals.
Refit or correct the sensor mounting and air gap, and remove any contamination.
Repair or replace a damaged trigger wheel, or correct the timing drive fault, as the model's procedure requires.
Rectify battery or charging faults to restore stable supply voltage.
Only after all else is ruled out, diagnose and replace the control unit as the manufacturer specifies.

Can I keep driving?

Medium severity

The car may start and run, but a missing position signal can cause stalling, hard starting or poor running, so get it fixed soon. Avoid long journeys if it stalls or runs badly, as that can be unsafe.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.