Mitsubishi Code P1391: Camshaft/Crankshaft Synchronization Problem

Technical Meaning

The Mitsubishi P1391 code on Mitsubishi vehicles indicates a fault in synchronization between the camshaft position sensor (CMP) and crankshaft position sensor (CKP) signals. This issue primarily affects:

• 🕒 Injection timing
• ⚡ Ignition control
• 🔧 Variable valve timing management (MIVEC on certain models)

Severity and Consequences

Level	Impact
Moderate	Unstable idle, slight power loss
High	Risk of stalling, catalyst damage

Mitsubishi-Specific Symptoms

• 🚗 Hard starting (especially on Lancer and Outlander)
• ⚠️ Check Engine light flashing + “Limp Home” mode
• ⛽ Noticeable increase in fuel consumption
• 🔊 Metallic knocking (if timing belt issue)

Model-Specific Causes

For 4G6 engines (Lancer EVO)

• Faulty CMP sensor (common issue)
• Premature timing belt wear
• Hydraulic tensioner problem

For 6B3 engines (Outlander)

• Connector corrosion (low sensor position)
• Excessive timing chain play
• MIVEC variable phasing failure

For 4N1 engines (recent ASX)

• Sensitivity to voltage variations
• ECM software update required

Diagnostic Procedure

Step 1: Electrical Check

1. Sensor testing:
   • CMP resistance: 400-800Ω (at 20°C)
   • CKP signal: Check for clean square wave
2. Wiring check:
   • Measure continuity between ECM and sensors
   • Verify no short circuit to ground

Step 2: Mechanical Check

• 🔍 Timing mark alignment
• ⚙️ Belt/chain tension (5-6mm max deflection)
• 🔧 Condition of sprockets and guides (abnormal wear)

Step 3: ECM Diagnosis

• 💻 Live data reading:
  • Real-time CMP/CKP comparison
  • Calculated phase shift verification
• 🔄 Software update (often required on Pajero IV)

Recommended Solutions

For Common Models

1. CMP sensor replacement (part # MD614602 for Lancer)
2. Connector cleaning + dielectric grease application
3. Timing adjustment with Mitsubishi special tools

For Recurring Problems

• Complete timing kit (including hydraulic tensioner)
• ECM reprogramming (update TSB 18-46-003)

Average Repair Costs

Intervention	Parts Cost	Labor
CMP Sensor	90-180€	0.8h
Timing Belt	120-250€	3.5h
Reprogramming	80-150€	1h

Specific Technical Tips

1. Always use OEM parts for sensors
2. Systematically check phasing after intervention
3. On Outlander PHEV: Disconnect HV power before diagnosis

Common Mistake: Neglecting water pump inspection during timing belt replacement (causing subsequent overheating)

⚠️ Warning: On Mitsubishi Diesel (4N1), this code may mask a rail pressure sensor problem. Always check associated codes.