Technical Meaning
The Jeep P1391 code on Jeep vehicles indicates a desynchronization between the camshaft position sensor (CMP) and crankshaft position sensor (CKP) signals. This fault disrupts engine management by affecting:
- ⏱️ Injection timing
- 🔥 Ignition control
- ⚙️ Valve timing
Severity and Consequences
| Level | Impact |
|---|---|
| Moderate | Unstable idle, power loss |
| High | Risk of stalling, catalytic damage |
Characteristic Symptoms
- 🚗 Hard starting (especially when cold)
- ⚡ Random misfires
- ⛽ Excessive fuel consumption up to 20%
- 🌡️ Abnormal overheating
- ⚠️ Check Engine light on + limp mode
Probable Causes Tree
Diagram
Advanced Diagnostic Procedure
1. Electrical Check (Tools: Multimeter, Oscilloscope)
- CMP resistance test: 200-1000Ω (refer to manual)
- CKP/CMP signal: Check pulse alternation
- Sensor power supply: 5V ±0.5V
2. Mechanical Check
- 🔧 Chain tension: Max 5mm play
- ⚙️ Timing mark alignment
- 🔍 Sprocket inspection (broken teeth)
3. ECM Diagnosis
- 💻 Software update
- 🔋 ECU power test (stable 12V)
Specific Jeep Cases
- Wrangler JK 3.8L: Recurrent CMP connector issue exposed to elements
- Grand Cherokee 4.7L: Premature chain tensioner wear
- Renegade 1.4T: Sensitivity to voltage variations
Average Repair Costs
| Intervention | Parts Cost | Labor |
|---|---|---|
| CMP replacement | 80-150€ | 0.5h |
| Chain replacement | 300-600€ | 4-6h |
| ECM reprogramming | 100-200€ | 1h |
Technical Tips
- Priority: Always check wiring first before condemning a sensor
- Tip: Use an oscilloscope to compare CMP/CKP signals
- Prevention: Replace chain every 150,000km on Pentastar engines
Common Mistakes
- 🔌 Neglecting sensor connector (frequent corrosion)
- ⏳ Forgetting to reset ECM adaptation after repair
- 🔄 Confusing with ignition coil problem
Important note: On recent Jeeps (after 2015), this code may require mandatory software update before any other intervention.