The Chrysler fault code P1391 indicates a problem in the synchronization circuit between the crankshaft sensor (CKP) and the camshaft sensor (CMP). This fault, specific to Chrysler, Dodge, and Jeep vehicles, can disrupt engine timing, leading to irregular idling, jerking, or even engine failure. Here is a detailed analysis.
The synchronization between the crankshaft sensor and the camshaft sensor is crucial for the proper functioning of the engine. For example, a misalignment in this synchronization can lead to poor performance, excessive fuel consumption, and even long-term internal engine damage. Additionally, it is important to understand that modern vehicles heavily rely on electronic systems and sensors to optimize their performance. A failure in these systems can therefore have serious and costly consequences.
Importance of Synchronization
Proper synchronization not only ensures the engine runs correctly but is also essential for reducing polluting emissions. Modern engine management systems use information from these sensors to adjust combustion parameters in real time. Consequently, a fault in one of these sensors can compromise the overall efficiency of the vehicle.
Meaning of Code P1391
- Description: “Intermittent Loss of CMP or CKP Sensor”.
- Main Cause: The engine control module (ECU) detects an abnormal discrepancy between the signals from the two sensors during startup or while driving.
- Consequences:
- Incorrect fuel injection and ignition timing.
- Risk of engine stalling or difficulty starting.
Common Symptoms
- Engine Shaking: Abnormal vibrations at idle or low RPM.
- Misfires: Hesitant acceleration and loss of power.
- Hard Starting: The engine cranks for a long time before starting.
- Engine Stalling: Sudden shutdown, especially when stopped.
- Check Engine Light Illuminated: Sometimes flashing in case of severe misfires.
Possible Causes
Other Associated Symptoms
In addition to the mentioned symptoms, a vehicle with code P1391 may also exhibit strange behaviors such as a knocking noise from the engine, a smell of unburned fuel, and higher than normal fuel consumption. These signs should be taken seriously as they may indicate more serious underlying problems.
- Electrical Problems:
- Damaged wires or corroded connectors on the CKP/CMP sensors.
- Short circuit or irregular voltage (e.g., blown fuse).
- Sensor Failures:
- Faulty camshaft sensor (CMP) or crankshaft sensor (CKP).
- Accumulation of metal debris on the sensors (magnetization).
- Mechanical Problems:
- Loose or misaligned timing belt.
- Damage to the distributor rotor (on equipped engines).
- PCM Module Faults: Rare, but possible (e.g., software error).
Diagnostic Procedure
- OBD-II Scanner:
- Read associated fault codes (e.g., P0340/P0335 confirming a sensor problem).
- Check live data: compare CKP/CMP signals.
- Visual Inspection:
- Check sensor cables and connectors (look for cracks, corrosion).
- Clean sensors (metal debris).
- Electrical Tests:
- Measure sensor resistance (CKP: 200–1000 Ω; CMP: 150–900 Ω).
- Test supply voltage (generally 5V or 12V).
- Mechanical Check:
- Inspect the timing belt and pulleys (alignment, wear).
Recommended Repairs
- Replace Faulty Sensors:
- Average cost: €70–150 (part + labor).
- Prefer OEM parts (Mopar).
- Repair Wiring:
- Replace damaged wires and clean connectors.
- Adjust Timing:
- If the belt is loose: replace the belt and realign the pulleys.
- Update PCM:
- If the problem persists, reprogram the ECU at a dealership.
Common Mistakes to Avoid
- Ignoring the Timing Belt: Misalignment often simulates a sensor fault.
- Neglecting Wiring: 80% of P1391 codes come from faulty electrical circuits, not the sensors themselves.
- Forgetting the Basics: Always check battery voltage (a weak battery distorts signals).
Prevention and Maintenance
Regular maintenance of your vehicle is key to avoiding problems such as code P1391. Make sure to check connectors and cables during each service. Additionally, regular cleaning of the sensors can help maintain their efficiency. It is also recommended to regularly change the fuel filter to prevent the accumulation of debris that could harm the sensors.
Estimated Costs
| Intervention | Price (parts + labor) |
|---|---|
| CMP/CKP Sensor Replacement | €100–250 |
| Wiring Repair | €80–150 |
| Timing Belt Replacement | €400–700 |
Conclusion
It is also vital to note that faulty sensors can sometimes be caused by other mechanical problems. For example, a faulty head gasket can lead to engine overheating, which could damage the sensors. Furthermore, the quality of the fuel used can also influence the proper functioning of the sensors. Using poor quality fuel can lead to a buildup of deposits that affects engine performance.
The Chrysler P1391 code points to a critical desynchronization between the engine position sensors. Although it can sometimes be resolved by simple cleaning or realignment, a thorough diagnosis is essential to avoid costly repairs. If you lack experience, consult a specialized Chrysler mechanic – delayed intervention can damage the catalytic converter or the engine.
Consequences of Non-Diagnosis
Failing to resolve a P1391 code can lead to serious consequences. An engine out of synchronization can suffer premature wear, which can cause costly repairs. Moreover, ignoring this problem can also lead to other fault codes that would further complicate diagnosis and repair. Therefore, it is crucial to act quickly at the first signs of failure.
Final Conclusion
In summary, the Chrysler P1391 code is a key indicator of potential problems in the engine synchronization system. Paying special attention to this code and performing proper diagnosis can save your engine from irreparable damage. If you are faced with this issue, do not hesitate to consult a professional to ensure the longevity of your vehicle.