Understand & Fix P0390: Camshaft Position Sensor B Circuit Intermittent (Bank 2) with iCarsoft CR Ultra P
If your vehicle’s check engine light flickers, you experience random misfires, or notice hesitation during acceleration that comes and goes, a diagnostic scan will likely return P0390. This OBD-II code stands for "Camshaft Position Sensor B Circuit Intermittent (Bank 2)"—a critical fault targeting the secondary camshaft position sensor (CMP B) in Bank 2 and its control circuit. The CMP sensor works with the Engine Control Module (ECM) to synchronize camshaft rotation with ignition timing and fuel injection. An "intermittent" error means the sensor’s signal cuts out, fluctuates, or becomes erratic under specific conditions (e.g., vibration, temperature changes), disrupting engine synchronization for Bank 2.
Basic scanners might only flag a "camshaft sensor error" but can’t capture intermittent signals, test circuit continuity under load, or validate sensor responsiveness across banks—leaving you guessing between a faulty CMP B sensor, damaged wiring, or a loose connector. The iCarsoft CR Ultra P, with its OE-level engine diagnostics, bi-directional control, and live data logging, solves this. Below, we break down P0390, its causes, symptoms, step-by-step resolution, and 8 FAQs to answer common troubleshooting questions.
What Is P0390?
P0390 focuses on the camshaft position sensor B (CMP B) in Bank 2—a component typically located near the Bank 2 camshaft (on the cylinder head or timing cover) in engines with dual banks (e.g., V6, V8). CMP B in Bank 2 works alongside CMP A (Bank 1) to provide redundant camshaft position data to the ECM, ensuring precise timing for each bank. The sensor generates a digital or analog signal as the camshaft rotates; when this signal becomes intermittent (drops out or fluctuates unexpectedly), the ECM triggers P0390. This issue often occurs under specific conditions—such as high RPM, wet weather, or engine vibration—making it harder to diagnose with basic tools.
Key Symptoms of P0390
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Flickering or Intermittent Check Engine Light: The light may turn on and off, especially during high-speed driving or acceleration.
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Random Misfires & Rough Idle: Erratic CMP B signals disrupt ignition timing for Bank 2, leading to shaking or uneven engine operation.
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Hesitation & Reduced Acceleration: The ECM loses sync with Bank 2’s camshaft, causing delayed power delivery when pressing the gas pedal.
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Engine Stalling: Severe intermittent signal loss can shut down Bank 2’s fuel injection/ignition, leading to sudden stalling.
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Poor Fuel Economy: Mismatched timing between banks increases fuel consumption by 12–18%.
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Failed Emissions Tests: Unburned fuel from misfires raises hydrocarbon emissions, resulting in compliance violations.
Common Causes of P0390
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Cause
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Description
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Faulty CMP B Sensor (Bank 2)
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A worn sensor (with degraded internal electronics) or one contaminated with oil/carbon buildup generates intermittent signals.
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Wiring/Circuit Issues
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Frayed wires, corroded connectors, or loose terminals in Bank 2’s CMP circuit that lose contact under vibration.
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Sensor Alignment Issues
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The CMP B sensor in Bank 2 is misaligned with the camshaft reluctor ring, causing intermittent signal loss.
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Timing Chain/Belt Wear
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A stretched timing chain/belt shifts Bank 2’s camshaft position relative to the sensor, disrupting signal transmission.
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ECM Malfunction
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Rarely, the ECM’s internal circuit for processing Bank 2’s CMP data fails, misinterpreting normal signals as intermittent.
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Why iCarsoft CR Ultra P Excels at Diagnosing P0390
The CR Ultra P outperforms basic tools with features tailored to intermittent multi-bank camshaft sensor diagnostics:
Dual-Bank Live Data Logging
Captures CMP A (Bank 1) and CMP B (Bank 2) signals simultaneously, highlighting Bank 2-specific intermittent dropouts.
Bi-Directional CMP Testing (Bank 2)
Activates Bank 2’s CMP B sensor manually under simulated load—distinguishes sensor faults from wiring issues.
Circuit Integrity Checks
Tests for loose connections, intermittent shorts, and continuity in Bank 2’s CMP wiring—critical for intermittent faults.
Topology Mapping
Visualizes engine bank configuration and wiring, making hidden damage in Bank 2 easy to locate.
Global Vehicle Coverage
Supports 200+ passenger vehicle brands and 2018+ models with dual-bank engines.
41 Hot Service Functions
Includes dual-bank CMP calibration, timing chain reset, and ECM reset—critical for post-repair validation.
Step-by-Step: Diagnose P0390 with iCarsoft CR Ultra P
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Confirm P0390 & Gather Data
Plug the CR Ultra P into your vehicle’s OBD-II port, power on the tool, and select AutoVIN Identify to auto-detect make, model, and bank configuration (e.g., V6 Bank 2 = passenger side).
Navigate to Engine > Fault Codes > Read Codes to confirm P0390. Tap Code Details for model-specific insights (e.g., "Ford F-150 V8: Camshaft Position Sensor B Circuit Intermittent (Bank 2); Signal Dropouts at 3000 RPM; Check Wiring or Sensor").
Use the CR Ultra P’s Data Logging function to record CMP A and CMP B signals during a test drive—captures Bank 2 dropouts basic scanners miss.
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Analyze Live CMP & Engine Data
Go to Engine > Live Data > Timing & Sensors and monitor three key metrics:
1. CMP B (Bank 2) Signal: Should show a steady digital/analog signal. Intermittent drops or fluctuations confirm P0390.
2. CMP A vs. CMP B Signals: Signals should be synchronized. A mismatch indicates a Bank 2-specific issue.
3. Bank 2 Misfire Count: Consistent Bank 2 misfires + CMP B fluctuations = P0390 root cause.
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Test the Camshaft Position Sensor B (Bank 2)
1. Use Bi-Directional Control > Engine > CMP Sensor Test (Bank 2): Send activation commands and simulate rotation. Intermittent responses = faulty sensor.
2. Locate Bank 2’s CMP B: Use the CR Ultra P’s Component Location tool (typically near the rear cylinder head for Bank 2).
3. Inspect & Test: Check for oil/carbon buildup or loose connectors. Use the CR Ultra P’s Resistance Test (should match OEM specs, e.g., 1k–5k ohms—fluctuating resistance = faulty sensor).
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Inspect Wiring, Connectors, & Timing Components
1. Wiring Check: Use Continuity Test on Bank 2’s CMP B wiring. Wiggle wires to simulate vibration—intermittent continuity = frayed/loose wiring.
2. Connector Check: Clean corroded terminals. Use the CR Ultra P’s Voltage Test to verify 12V power and ground to the sensor.
3. Timing Check: Inspect timing chain/belt for wear. Use the CR Ultra P’s Camshaft Timing Test (Dual Bank) to verify alignment.
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Repair & Clear the Code
- Replace Bank 2’s CMP B sensor if tests confirm it’s faulty (use OEM-compatible sensors for cross-bank signal accuracy).
- Repair damaged wiring, clean connectors, or adjust sensor alignment. Replace worn timing chain/belt if required.
- Use the CR Ultra P to Clear Codes and run a Dual-Bank Timing Synchronization Test. Log signals during a follow-up test drive to confirm no Bank 2 dropouts remain.
FAQs: P0390 Troubleshooting
Can I drive with P0390?
Short trips are risky—intermittent stalling and misfires increase accident risk. Use the CR Ultra P’s data logging to capture Bank 2’s signal dropouts, then repair before driving long distances.
How much does it cost to fix P0390?
A new CMP B sensor (Bank 2) costs $50–$200, plus $120–$250 for labor (higher if Bank 2’s sensor is hard to access). Using the CR Ultra P to diagnose yourself saves on shop diagnostic fees ($100–$150).
Why does P0390 keep returning after clearing it?
The root cause is intermittent. Common culprits: loose wiring that shifts under vibration, a misaligned sensor, or a worn timing chain. Use the CR Ultra P’s data logging to track when the code reappears (e.g., only at high RPM = wiring rub damage).
What’s the difference between P0390 (Bank 2, CMP B) and P0340 (Bank 1, CMP A)?
P0390 targets Bank 2’s secondary camshaft sensor (CMP B), while P0340 targets Bank 1’s primary sensor (CMP A). The CR Ultra P’s AutoVIN Identify clarifies bank locations for your specific vehicle.
How do I distinguish between a faulty CMP B (Bank 2) and wiring?
Use the wiggle test: Wiggle Bank 2’s CMP B wiring while monitoring signals—intermittent dropouts = wiring issue; Wiggle the sensor connector—no dropouts + erratic signals = faulty CMP B sensor.
Do I need to calibrate the CMP sensor after replacement?
Yes—use the CR Ultra P’s CMP Sensor Calibration (Dual Bank) (under Special Functions) to sync the new Bank 2 sensor with the ECM. This ensures proper timing alignment between banks.
Can wet weather cause P0390?
Yes—moisture can corrode Bank 2’s CMP connector or short wiring, leading to intermittent signals. Use the CR Ultra P’s Voltage Test to check for water damage in the circuit.
Will P0390 fail an emissions test?
Yes—Bank 2 misfires from intermittent timing issues increase emissions. Fix P0390 with the CR Ultra P, drive 50+ miles to reset readiness monitors, and retest to ensure compliance.
Conclusion
P0390’s intermittent camshaft position sensor B fault in Bank 2 is tricky to diagnose, but the iCarsoft CR Ultra P simplifies the process with dual-bank data logging, bi-directional testing, and circuit validation. It ensures you fix the root cause—whether it’s a faulty sensor, loose wiring, or timing misalignment—instead of just clearing the code.
With a 10.1-inch HD touchscreen, 12600mAh long-life battery, and 3 years of free software updates, the CR Ultra P is a must-have for DIYers and mechanics working on dual-bank engines. Resolve P0390, restore cross-bank synchronization, and drive without misfires—all with one professional-grade diagnostic scanner.
