P0391 Code: Camshaft Position Sensor “B” Circuit Range/Performance (Bank 2) – Full Diagnose & Fix with iCarsoft CR Max P
If your engine idles roughly, hesitates under acceleration, wastes fuel, or illuminates the check engine light, the P0391 fault code signals a critical timing issue. P0391 stands for Camshaft Position Sensor “B” Circuit Range/Performance (Bank 2), an OBD‑II powertrain code triggered when the Powertrain Control Module (PCM) detects an abnormal, unstable, or out‑of‑range signal from Camshaft Position Sensor “B” on engine Bank 2. This sensor synchronizes fuel injection and ignition timing; a range/performance fault disrupts engine efficiency, reduces power, and can lead to costly internal damage if ignored. Basic code readers only confirm the code, but the iCarsoft CR Max P professional diagnostic tool lets you pinpoint sensor failure, wiring issues, or timing inconsistencies and clear P0391 quickly and safely at home.
What Is the P0391 Fault Code?
P0391 is officially defined as: Camshaft Position Sensor “B” Circuit Range/Performance (Bank 2).
The PCM monitors the camshaft position signal to sync valve timing, fuel delivery, and spark. When Sensor B on Bank 2 sends a signal that is out of the factory voltage range, erratic, or non‑responsive, the PCM logs P0391 and enables protective engine modes.
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Bank 2: The cylinder bank that does NOT include cylinder #1
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Sensor “B”: Usually the exhaust camshaft position sensor
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Range/Performance: Signal voltage is too high, too low, intermittent, or does not match crankshaft position
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Effect: Poor idle, reduced power, misfires, increased emissions, and potential timing damage
Key Symptoms of P0391
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Check engine light (MIL) illuminated
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Rough idle or unstable RPM at a stop
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Sluggish acceleration and lack of power
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Engine hesitation or stumbling under load
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Reduced fuel economy (10–20% higher consumption)
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Cold-start difficulty or intermittent stalling
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Misfires at low speed or idle
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Vehicle may enter limp‑mode to prevent damage
Common Causes of P0391
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Faulty or degraded Camshaft Position Sensor “B” (most common)
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Damaged, frayed, or shorted wiring in the sensor circuit
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Corroded, loose, or oil‑contaminated electrical connectors
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Weak or dying vehicle battery causing low voltage
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Damaged reluctor wheel or timing alignment issues
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Oil contamination blocking the sensor signal
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Faulty PCM (very rare)
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Outdated PCM calibration or software glitch
Why iCarsoft CR Max P Is the Best Tool for P0391
Read & Clear P0391
Supports all manufacturer-specific engine timing fault codes.
Live Cam/Crank Sync Data
View real-time sensor voltage and signal quality.
Bi-Directional Active Tests
Verify sensor response and circuit integrity instantly.
Auto VIN Detection
Loads your exact engine wiring and sensor location automatically.
PCM Reset & Timing Relearn
Reset the computer and restore factory timing behavior.
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Ford, GM, Toyota, Honda, VW, BMW, Mercedes, and more.
Lifetime Free Wi-Fi Updates
No subscriptions — always updated for new models and codes.
HD Touchscreen
Intuitive for DIYers and professional technicians.
Step-by-Step: Diagnose & Clear P0391 with iCarsoft CR Max P
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Plug iCarsoft CR Max P into the OBDII port under the dashboard.
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Turn ignition to ON (engine off).
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Select your vehicle or use Auto VIN for automatic detection.
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Go to Engine System > Camshaft/Crankshaft Sensors and run Full System Scan.
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Confirm P0391: Camshaft Position Sensor “B” Circuit Range/Performance (Bank 2).
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Enter Live Data to monitor Sensor B voltage and signal quality.
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Use Active Test to verify sensor function and circuit health.
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Inspect wiring, connectors, or replace the sensor as needed.
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Use Clear Fault Codes to erase P0391.
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Perform PCM Reset and test‑drive to confirm normal operation.
Real Customer Reviews
“P0391 caused rough idle and bad MPG on my Toyota. Dealer wanted $400 to diagnose. My iCarsoft CR Max P showed a bad cam sensor on Bank 2. Replaced it for $65, cleared the code, saved over $1,000.”
— Michael T., DIY Mechanic
“I use iCarsoft CR Max P in my shop for P0391 weekly. Live cam/crank sync data finds the problem in 2 minutes. Cuts diagnostic time by 70%.”
— Lisa S., ASE Certified Technician
“My Ford Edge threw P0391 and hesitated bad. The scanner found a corroded connector. Cleaned it, reset the PCM, runs perfect. No more dealership bills.”
— Kevin D., Ford Owner
“P0391 kept coming back after sensor swap. This tool revealed a weak battery. Replaced battery, cleared code, fixed forever. Best tool I own.”
— Tom L., Repair Shop Owner
“I’m a backyard mechanic and this tool solved my P0391 in under 30 minutes. Live data made it so easy. Highly recommend.”
— Amanda R., DIY Car Enthusiast
FAQ: P0391 & iCarsoft CR Max P
1. What does P0391 mean in simple terms?
P0391 means the PCM detects an unreliable or out‑of‑range signal from Camshaft Position Sensor “B” on Bank 2, disrupting engine timing.
2. Can I drive with P0391?
You can drive short distances, but long‑term use is not recommended due to misfires, poor fuel economy, and risk of timing damage.
3. Will a basic OBD scanner fix P0391?
No. Basic scanners only read the code. You need live sensor data and bi‑directional tests from a professional tool like iCarsoft CR Max P.
4. What is the most common fix for P0391?
Replacing Camshaft Position Sensor B resolves about 70% of cases. Wiring and connector issues make up most of the rest.
5. How do I know if it’s the sensor or wiring?
Use iCarsoft CR Max P to view live camshaft sensor data. If the signal is flat or erratic, test the circuit to distinguish sensor vs. wiring fault.
6. Can a weak battery cause P0391?
Yes. Low or unstable voltage often triggers false range/performance codes like P0391.
7. Do I need to reset the PCM after fixing P0391?
Yes. The iCarsoft CR Max P lets you reset the PCM and perform camshaft timing relearn for proper operation.
8. Is iCarsoft CR Max P worth buying for P0391?
Absolutely. It diagnoses P0391 in minutes, saves hundreds in shop fees, and works on hundreds of systems.
Why You Must Fix P0391 Immediately
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Premature timing chain or belt wear
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Engine misfires and internal damage
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Catalytic converter overheating and failure
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Severe fuel economy loss
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Complete loss of power and limp‑mode events
Final Thoughts
P0391 – Camshaft Position Sensor “B” Circuit Range/Performance (Bank 2) – is a common but serious engine code that threatens performance and reliability. With the iCarsoft CR Max P, you can diagnose, repair, and clear P0391 at home without expensive dealership labor.
Don’t let a faulty cam sensor damage your engine or waste gas. Get the iCarsoft CR Max P and restore smooth, efficient performance today.
Get iCarsoft CR Max P Now →
Disclaimer: This guide is for informational purposes only. Always consult your vehicle’s service manual or a certified automotive technician before performing engine repairs. iCarsoft is not responsible for damage from improper tool use or vehicle maintenance.
