P1391 Code: Intermittent Loss Of CKP Or CMP Signal (Dodge/Chrysler)

P1391 is a manufacturer-specific diagnostic trouble code (DTC) used exclusively by Dodge and Chrysler vehicles. This code signals that your engine control module (ECM) has detected an intermittent loss of signal from either the crankshaft position sensor (CKP) or the camshaft position sensor (CMP). These sensors are critical for proper engine timing and fuel injection, so signal loss can cause drivability issues ranging from mild hesitation to severe misfires.

What Does P1391 Mean?

The P1391 code is a Dodge/Chrysler-specific diagnostic trouble code that indicates the ECM has detected intermittent signal dropout from the CKP or CMP sensor. Unlike a hard fault code that triggers when a sensor completely fails, P1391 specifically flags intermittent signal loss—meaning the sensor works sometimes but not consistently.

The crankshaft position (CKP) sensor monitors the rotational speed and position of the crankshaft, while the camshaft position (CMP) sensor tracks the camshaft’s position. Both sensors send critical timing signals to the ECM, which uses this data to:

• Control fuel injection timing and duration
• Manage spark plug ignition timing
• Monitor engine speed (RPM)
• Detect engine misfires

When either sensor loses signal intermittently, the ECM cannot reliably calculate proper engine timing, resulting in the P1391 code being stored.

Common Symptoms

Drivers experiencing P1391 may notice one or more of the following symptoms:

• Check Engine Light (CEL) – Illuminated on the dashboard
• Rough idle – Engine vibrates or feels unstable at stops
• Hesitation during acceleration – Loss of power when pressing the gas pedal
• Intermittent stalling – Engine shuts off unexpectedly while driving
• Misfires – Engine runs rough, especially under load
• Difficulty starting – Engine cranks but takes longer to fire up
• Poor fuel economy – Reduced miles per gallon due to inefficient combustion
• Limp mode activation – Vehicle enters reduced-power mode to protect the engine

The key characteristic of P1391 is that symptoms are intermittent—they may come and go, making diagnosis challenging. The vehicle might run perfectly fine one moment and then hesitate or stall the next.

Possible Causes (Ranked by Frequency)

1. Faulty CKP or CMP Sensor – The most common cause. Sensors degrade over time due to heat, vibration, and contamination, causing intermittent signal loss.
2. Corroded or Loose Sensor Connectors – Corrosion, moisture, or loose connections at the sensor plug prevent reliable signal transmission.
3. Damaged Sensor Wiring – Frayed, pinched, or corroded wiring between the sensor and ECM interrupts the signal.
4. Engine Oil Contamination – Dirty oil or metal particles can coat the sensor tip, blocking the magnetic signal.
5. Sensor Gap Too Large – If a sensor mounting bracket is bent or loose, the sensor may sit too far from the trigger wheel, weakening the signal.
6. Timing Chain or Belt Wear – Excessive wear can cause timing component wobbling, affecting sensor signal consistency.
7. ECM Software Issues – Rarely, outdated or corrupted ECM firmware may misinterpret valid sensor signals.
8. Electromagnetic Interference (EMI) – Aftermarket electrical components or damaged shielding can introduce noise into sensor circuits.

Diagnostic Steps

Follow these steps to diagnose P1391:

Step 1: Verify the Code and Scan for Related Codes

Use a quality OBD-II scanner to confirm P1391 is present. Check for related codes such as:

• P0335 (CKP Sensor Circuit Malfunction)
• P0340 (CMP Sensor Circuit Malfunction)
• P0016 (Crankshaft/Camshaft Timing Misalignment)

Related codes help narrow down whether the issue is with the CKP or CMP sensor.

Step 2: Visual Inspection

Locate both the CKP and CMP sensors (consult your vehicle’s service manual for exact locations). Inspect for:

• Corrosion or discoloration on connectors
• Loose or disconnected wiring
• Damaged or pinched sensor cables
• Oil or coolant leaks near sensors
• Bent or misaligned sensor brackets

Step 3: Clean Sensor Connectors

Disconnect the sensor connectors and inspect the pins for corrosion. Clean with electrical contact cleaner and a soft brush. Reconnect firmly and test-drive to see if the code clears.

Step 4: Check Sensor Resistance and Voltage

Using a multimeter, measure the sensor’s resistance and voltage output according to manufacturer specifications (values vary by sensor type). Compare readings to the service manual. Inconsistent or out-of-spec readings indicate a faulty sensor.

Step 5: Inspect Wiring and Connectors

Trace the sensor wiring from the sensor to the ECM. Look for:

• Pinched or crushed wires
• Rodent damage
• Loose connections at the ECM
• Damaged wire insulation

Repair or replace damaged wiring as needed.

Step 6: Check Sensor Gap and Mounting

Ensure the sensor is properly mounted and the gap between the sensor tip and the trigger wheel is within specification (typically 0.020–0.050 inches). Adjust or tighten the mounting bracket if loose.

Step 7: Replace the Faulty Sensor

If all checks point to a bad sensor, replace it with a manufacturer-recommended part. Clear the code and test-drive to confirm the fix.

Step 8: Check Engine Oil Condition

If the sensor appears coated with oil residue, perform an oil and filter change. Contaminated oil can cause intermittent sensor faults.

Repair Cost Estimates

Repair costs for P1391 vary depending on the root cause and your vehicle’s make/model:

• Sensor Replacement: $150–$400 per sensor (parts + labor). CKP sensors typically cost $50–$200; CMP sensors range $75–$300. Labor is usually 0.5–1.5 hours.
• Connector/Wiring Repair: $50–$200. Simple connector cleaning or re-seating is inexpensive; wiring replacement costs more.
• Wiring Harness Replacement: $200–$600 if extensive wiring damage is found.
• ECM Reprogramming: $100–$300 if software issues are suspected (rare).

DIY Potential: If you have mechanical experience, sensor replacement and connector cleaning are manageable DIY tasks. However, wiring repairs and ECM work should be left to professionals.

Can I Still Drive?

P1391 is a moderate-severity code. Whether you can safely drive depends on the symptoms:

• Safe to Drive (Temporarily): If you experience only occasional hesitation or a check engine light with no stalling, you can drive carefully to a repair shop. Avoid highway driving and heavy acceleration.
• Not Safe to Drive: If the engine stalls intermittently, misfires severely, or enters limp mode, do not drive. The risk of sudden engine shutdown or loss of power steering/brakes is too high. Have the vehicle towed to a mechanic.

Intermittent signal loss can worsen over time, so address P1391 promptly to avoid more serious engine damage or safety hazards.

Frequently Asked Questions