Honda Code P1391: CKP/CMP Synchronization Problem

(Intermittent Loss of CMP or CKP Signal)

Technical Meaning

Fault: The PCM detects an intermittent loss of synchronization between the crankshaft position sensor (CKP) and the camshaft position sensor (CMP).
Impact: Ignition and injection desynchronization → Risk of stalling, misfires, or failure to start.
Honda Specificity: On i-VTEC engines, this code may disable the variable camshaft system, reducing power and fuel economy.

Affected Honda Models

Model	Common Engines	Years
Honda Civic	1.6L, 1.7L, 2.0L (D-Series, R-Series)	2001-2015
Honda Accord	2.4L K24, 3.0L/3.5L V6 (J-Series)	2003-2017
Honda CR-V	2.0L/2.4L (K-Series)	2002-2016
Honda Odyssey	3.5L J35 V6	2005-2020
Honda Pilot	3.5L J35 V6	2006-2015

Common Symptoms

⚠️ Sudden stalling at idle (especially with air conditioning activated).
🔧 Extended cranking (engine turns for 5-10 seconds before starting).
⚡ Misfires during acceleration (feeling of hiccups).
📉 Loss of power (i-VTEC disabled as a safety measure).
💡 Check engine light on + VSA light sometimes activated.

Specific Causes in Hondas

Electrical Problems (60-70% of cases):
- CKP wires chewed by the fan (especially on Civic/CR-V).
- Oxidized CMP connector (low location, exposed to water/snow).
- Blown fuse (check the fuse box under the steering wheel: PCM 15A Fuse).
Mechanical Failures:
- Damaged CKP reluctor wheel (bent or rusty teeth, common on Civic).
- Stretched timing chain (high-mileage K24/J35 engines >150,000 km).
- Metal debris on CKP sensor (engine or transmission wear).
Other Causes:
- CMP valve cover gasket leak (oil floods the sensor on Accord/CR-V).
- Faulty main relay (PGM-FI, blocks sensor power supply).

Step-by-Step Diagnosis

Honda-Specific OBD2 Scan:
- Use an HDS (Honda Diagnostic System) scanner to read related codes:
  - P0335 (CKP), P0340 (CMP), P2646 (VTEC problem).
- Check the “CMP Pattern” in live data: it should be stable.
Physical Inspection:
- Sensor locations:
  CKP: Behind the engine pulley (transmission side).
  CMP: On the cylinder head, under the valve cover (Accord) or near the pulley (Civic).
- Critical points:
  - CKP wires rubbing against the fan (Civic).
  - Oil leak at CMP gasket (CR-V/Accord).
Electrical Tests:SensorVoltage (V)Resistance (Ω)CKP5V or 12V350–700 ΩCMP5V250–1,000 Ωℹ️ Disconnect the connector to measure.

Recommended Repairs

Solution	Estimated Cost (USD)	Urgency
Replace CMP sensor	$50–120	🔧🔧
Repair CKP harness	$70–180	🔧🔧
Clean CKP reluctor wheel	$0 (DIY)	🔧
Replace CMP gasket	$30–90	🔧
Adjust/replace timing chain	$600–1,200	⚠️⚠️

Concrete example: On a Honda Civic 1.7L, the CKP harness passes near the fan → Wires severed. Solution: Replace the harness + add protective sleeving.

Mistakes to Absolutely Avoid

🚫 Ignoring the timing chain: A stretched chain is common on K24s (Accord/CR-V) and triggers P1391 + P0016.
🚫 Forgetting the PGM-FI relay: Test it before replacing a sensor (under the dashboard on the driver’s side).
🚫 Neglecting sealing gaskets: An oil leak quickly destroys the new CMP sensor.

Honda-Specific Technical Tips

Diagnostic Tools:
- HDS scanner mandatory for CKP relearn after replacement (“CKP Pattern Clear” procedure).
- Economical alternative: Launch or Autel scanner compatible with Honda.
Emergency Procedure:
- If the engine stalls: Turn the ignition off for 10 seconds → Restart (the PCM attempts a resynchronization).
Quick Check:
- Test the main relay (PGM-FI): Listen for a click when turning the ignition on, or measure 12V at the CMP/CKP connector.

⚠️ Safety Warning:

An untreated P1391 can cause a complete breakdown (engine no longer starts).

If the VSA light comes on, check the stability control system (disabled as a safety measure).

*Source: Honda Workshop Manual (HDS), technical service bulletin TSB 12-045 (2012) for recurring issues on CR-V 2010-2014.*

ℹ️ Note: On J35 V6 engines (Odyssey/Pilot), code P1391 is often related to a faulty VTEC solenoid → Check it before replacing the CMP!