The P1391 trouble code is a manufacturer-specific diagnostic code that typically indicates an intermittent loss of signal from either the camshaft position (CMP) sensor or the crankshaft position (CKP) sensor. This code is commonly found in Chrysler, Jeep, and Dodge vehicles, particularly those with the 4.0L inline-six engine. When the powertrain control module (PCM) detects an inconsistent or missing signal from these critical sensors, it triggers the P1391 code and usually illuminates the check engine light.
| P1391 Code Meaning | P1391 Code Common Causes |
|---|---|
| Intermittent loss of CMP or CKP sensor signal | Faulty CMP or CKP sensor |
| PCM unable to synchronize engine timing | Wiring issues in CMP or CKP circuits |
| Potential engine performance issues | Worn distributor or damaged reluctor wheel |
| May affect fuel economy and emissions | Electrical system problems (low voltage) |
| Can lead to no-start conditions if severe | PCM malfunction (rare) |
Symptoms of P1391 Code
When a vehicle experiences a P1391 code, several symptoms may manifest:
- Illuminated check engine light
- Engine misfires or rough idle
- Stalling or hard starting
- Reduced engine performance
- Poor fuel economy
- Intermittent loss of power while driving
- In severe cases, the engine may not start at all
These symptoms can vary in severity and may not always be present, making diagnosis challenging. The intermittent nature of the P1391 code means that the vehicle might run normally at times, only to exhibit problems sporadically.
Technical Explanation of P1391
The P1391 code is closely related to the engine’s timing and synchronization systems. The CMP and CKP sensors play crucial roles in providing the PCM with information about the engine’s rotational position and speed. This data is essential for proper fuel injection timing, ignition timing, and overall engine management.
The CKP sensor monitors the position and rotational speed of the crankshaft, while the CMP sensor tracks the position of the camshaft. Together, these sensors enable the PCM to determine the engine’s exact position in the four-stroke cycle (intake, compression, power, exhaust) for each cylinder.
When the PCM detects an intermittent loss of signal from either of these sensors, it sets the P1391 code. This loss of signal can be due to various factors, including sensor failure, wiring issues, or problems with the components these sensors monitor, such as the reluctor wheel or distributor.
Step-by-Step Diagnosis of P1391
To diagnose the P1391 code effectively, follow these steps:
- Verify the code: – Use an OBD-II scanner to confirm the P1391 code and check for any additional codes that may be present.
- Check for Technical Service Bulletins (TSBs): – Research if there are any TSBs related to P1391 for your specific vehicle make and model.
- Inspect wiring and connections: – Examine the wiring harnesses and connectors for the CMP and CKP sensors. – Look for signs of damage, corrosion, or loose connections. – Repair or replace any damaged wiring or connectors.
- Test sensor signals: – Use an oscilloscope or graphing multimeter to test the output signals of both the CMP and CKP sensors. – Compare the readings to manufacturer specifications.
- Check sensor mounting and alignment: – Ensure that both sensors are securely mounted and properly aligned with their respective targets (reluctor wheel or distributor).
- Inspect the distributor (if applicable): – On vehicles with distributors, check for wear or damage that could affect sensor readings.
- Verify reluctor wheel condition: – Inspect the reluctor wheel (also known as a tone ring) for damage or missing teeth.
- Test the charging system: – Ensure the alternator is providing adequate voltage, as low system voltage can cause sensor reading issues.
- Check for engine mechanical issues: – Verify proper timing chain tension and camshaft timing.
- Perform advanced PCM diagnostics: – If all other tests pass, consider testing the PCM or having it professionally diagnosed.
Solution Methods for P1391
Based on the diagnosis, here are potential solutions for the P1391 code:
- Replace faulty sensors:
- If either the CMP or CKP sensor is found to be defective, replace it with a high-quality OEM or equivalent aftermarket part.
- Repair wiring issues:
- Fix any damaged wiring, replace corroded connectors, and ensure all connections are secure.
- Replace or repair the distributor:
- If wear or damage is found in the distributor, replace it or have it professionally rebuilt.
- Replace the reluctor wheel:
- If the reluctor wheel is damaged, it will need to be replaced. This may involve significant labor, especially if it’s located inside the engine.
- Address charging system problems:
- Replace a faulty alternator or voltage regulator if low system voltage is detected.
- Correct engine mechanical issues:
- If timing chain issues are found, they must be addressed. This may involve replacing the timing chain, tensioners, or even the camshaft in severe cases.
- Update PCM software:
- In some cases, a PCM software update may resolve intermittent sensor reading issues.
- Replace PCM:
- As a last resort, if all other solutions fail and the PCM is determined to be at fault, it may need to be replaced and programmed.
Cost Estimates for P1391 Repairs
The cost to repair a P1391 code can vary widely depending on the root cause and the vehicle make and model. Here are some estimated ranges:
- Sensor replacement: $100 – $300
- Wiring repair: $50 – $200
- Distributor replacement: $200 – $500
- Reluctor wheel replacement: $300 – $1000+
- Alternator replacement: $200 – $600
- Timing chain replacement: $500 – $2000+
- PCM replacement and programming: $500 – $1500
These estimates include parts and labor. DIY repairs can significantly reduce costs, but some repairs may require specialized tools or expertise.
Warnings and Recommendations
Warning: Ignoring the P1391 code can lead to engine damage, reduced fuel efficiency, and potential safety hazards due to unexpected stalling or loss of power.
Recommendations:
- Always use high-quality replacement parts, preferably OEM or equivalent.
- If you’re unsure about performing any diagnostic steps or repairs, consult a professional mechanic.
- After repairs, clear the code and perform a thorough test drive to ensure the issue is resolved.
- Regular maintenance, including timely replacement of wear items like spark plugs and ignition components, can help prevent P1391 and related issues.
- When replacing sensors, be careful not to damage the reluctor wheel or other sensitive components.
- If the problem persists after initial repairs, consider seeking a second opinion or consulting with a dealer technician familiar with your specific vehicle model.
In conclusion, the P1391 code, while often challenging to diagnose due to its intermittent nature, is typically resolvable through careful diagnosis and targeted repairs. By following the steps outlined in this guide, vehicle owners and DIY mechanics can effectively address this issue and restore proper engine operation. Remember that proper diagnosis is key to avoiding unnecessary parts replacement and ensuring a successful repair.
Frequently Asked Questions About P1391
- Can I drive my vehicle with a P1391 code?
While possible, it’s not recommended. The code indicates potential engine timing issues that could lead to poor performance or stalling. - How urgent is it to address a P1391 code?
It’s important to address it promptly. Ignoring it can lead to worsening performance and potential engine damage. - Will a P1391 code clear itself?
The code may clear temporarily if the issue is intermittent, but it will likely return if the underlying problem isn’t fixed. - Can a bad battery cause a P1391 code?
Yes, a weak battery or charging system issues can cause sensor reading problems that trigger P1391. - Is P1391 specific to certain vehicle makes?
While it’s most common in Chrysler, Jeep, and Dodge vehicles, similar codes can appear in other makes with different code numbers. - Can dirty oil cause a P1391 code?
Indirectly, yes. Dirty oil can cause timing chain wear, which may affect sensor readings and trigger P1391. - How long does it typically take to diagnose and repair a P1391 code?
Diagnosis can take 1-2 hours, while repair time varies from 30 minutes for a simple sensor replacement to several hours for more complex issues. - Are aftermarket sensors reliable for fixing P1391?
Quality aftermarket sensors can be reliable, but OEM parts are often recommended for the most consistent performance.