P1387
CYP Sensor B No Signal.
- Acura
- 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 Acura (and Honda) means the engine control unit is getting no signal from CYP Sensor B. CYP stands for cylinder position, a sensor that reads a camshaft-driven reluctor so the ECU can tell which cylinder is on which stroke. The code sets when the crankshaft is turning but the ECU sees no pulses from this sensor. Which physical sensor is 'B' depends on the model and engine, so check the factory information for your car.
Symptoms
- Malfunction indicator lamp on
- Long cranking or hard starting
- Engine stalls or cuts out unexpectedly
- Rough running, misfire or poor fuelling
- Loss of power or hesitation
- Engine will not start in some cases
Possible causes
- Faulty CYP sensor B (internal failure or no output)likely
- Damaged, chafed or open-circuit wiring between the sensor and the ECU (signal, power or ground)likely
- Corroded, loose or contaminated sensor connector or ECU connectorlikely
- Damaged or loose sensor mounting, or incorrect air gap to the reluctorpossible
- Camshaft reluctor or drive damaged, or timing belt or chain jumped or wornpossible
- Low or unstable supply voltage from a weak battery or poor earthspossible
- Fault inside the engine control unitrare
How to diagnose
- Read all stored and pending codes and the freeze frame data. Note engine speed, coolant temperature and whether other cam or crank sensor codes are present.
- Clear the code and see if it returns immediately on cranking or only intermittently.
- Visually inspect the sensor, its wiring and connectors for oil, heat damage, chafing, corrosion and bent or pushed-back pins.
- Check the battery condition and charging voltage, plus the main engine earths.
- Using the factory wiring diagram for your model, check the sensor supply, ground and signal wires for continuity, shorts and voltage.
- Watch the sensor signal with a scope or live data while cranking to confirm pulses are present and clean.
- Check the sensor is secure with the correct air gap, and inspect the reluctor or trigger wheel for damage.
- If the signal is still missing or erratic, verify the timing belt or chain and cam timing marks as per the model's procedure.
How to fix
- Replace the CYP sensor B if it is confirmed faulty or giving no output.
- Repair or replace damaged wiring and clean or renew corroded connector terminals.
- Refit or secure the sensor correctly and renew its seal or mounting if damaged.
- Repair or replace a damaged reluctor or trigger wheel, and correct the cam timing if it has slipped.
- Fix battery, charging or earth faults that cause unstable voltage.
- Repair or replace the ECU only after the wiring and sensor are proven good and the factory procedure calls for it.
Can I keep driving?
Medium severity
Avoid driving more than necessary, as the engine may stall or fail to restart, which can be unsafe in traffic. Get it diagnosed soon, and stop driving if it cuts out or runs badly.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.