Camshaft Position Sensor B Circuit Range/Performance (Bank 2)
The P0391 code means the vehicle's onboard diagnostic system has detected: Camshaft Position Sensor B Circuit Range/Performance (Bank 2). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $60 - $600 (parts and labor)
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What Are the Symptoms of P0391?
- Check Engine Light on
- Rough idle or hesitation
- Reduced performance
- Possible timing chain noise
What Causes P0391? (Most Likely First)
- Degraded cam sensor B signal quality Very High
- Timing chain stretch on Bank 2 High
- Incorrect sensor air gap Moderate
- PCM calibration issue Low
Can I Still Drive with P0391?
Short distances only. P0391 is rated moderate severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Common Fixes by Vehicle
What techs usually find when diagnosing P0391 on specific vehicles — tap your vehicle for the fix and the exact part:
2005-2015 Nissan Altima/Maxima/Pathfinder VQ35/VQ40 Moderate DIY
Bank 2 (passenger side) camshaft position sensor B circuit fault. Replace the CMP sensor on the rear of the passenger-side cylinder head. Use Nissan OEM or Hitachi unit; generic sensors commonly re-trigger within weeks.
Labor: 45-60 min2004-2014 Ford F-150/Explorer/Mustang 4.0L/3.7L V6 Moderate DIY
Bank 2 cam sensor B circuit malfunction — replace the cam position sensor on the passenger side head. On 4.0L SOHC, also inspect for timing chain stretch (a well-known 4.0L SOHC failure).
Labor: 45 min-1 hr2007-2013 Infiniti G35/G37/FX35 VQ35/VQ37 Moderate DIY
Bank 2 CMP-B fault — replace cam sensor with OEM Nissan/Hitachi. Inspect wiring harness under the intake for damage from rodent chewing (common VQ35 complaint). If chain stretch is suspected via long crank times, timing chain service is due.
Labor: 1-1.5 hrFrequently Asked Questions
Can timing chain stretch cause P0391?
Yes, a stretched timing chain alters the cam-to-crank relationship, causing the sensor signal to fall outside the expected range.
Is P0391 a sensor or mechanical problem?
It can be either. Start by checking the sensor, but if the sensor is good, investigate the timing chain.
How do I check for timing chain stretch?
Use an oscilloscope to compare crank and cam sensor waveform timing, or check for chain slack with a tensioner gauge.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P0391?
-
Compare cam sensor B signal to spec on oscilloscope.
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Check timing chain slack on Bank 2.
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Verify sensor air gap.
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Compare Bank 1 and Bank 2 sensor signals.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Which Vehicles Commonly Get P0391?
- 2010-2020 Toyota Highlander (3.5L V6)
- 2012-2019 Nissan Maxima (3.5L V6)
- 2008-2018 Ford Explorer (3.5L V6)
- 2011-2020 Honda Pilot (3.5L V6)
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