P0390 — Camshaft Position Sensor “B” Circuit #

Please note: The wording for this fault code may differ depending on your vehicle’s manufacturer.

• Camshaft Position Sensor “B” Circuit (Generic OBD-II)
• Exhaust Camshaft Position Sensor Circuit (Ford, Toyota)
• Camshaft Position Sensor B Circuit Bank 1 (Honda, Nissan, Hyundai, Kia)
• Cam Position Sensor B Circuit Malfunction (GM, Chrysler, Subaru)
• Exhaust CMP Sensor Circuit Malfunction (Mazda)

Summary of Code P0390 #

The P0390 diagnostic trouble code (DTC) is set when the Engine Control Module (ECM), essentially your vehicle’s main computer, detects a problem in the electrical circuit of the Camshaft Position Sensor “B”. This sensor monitors the position of the exhaust camshaft (often on Bank 1, which is the side of the engine with cylinder #1). The sensor provides crucial data for precise engine timing and fuel injection. When the ECM notices an abnormal or missing signal from this sensor, it triggers P0390, potentially affecting engine performance, emissions, and drivability. The exact impact varies depending on your car’s make and model, but prompt diagnosis is always recommended.

Frequent Symptoms for Code P0390 #

A faulty camshaft position sensor “B” circuit doesn’t always cause dramatic symptoms, but if you’re paying attention, your vehicle will likely give you some hints. You might notice your check engine light illuminating, which is the most obvious sign. Other symptoms can range from subtle to severe, including engine hesitation or rough idling. Here’s what to watch for:

• Check Engine Light illuminated
• Rough idle or fluctuating engine RPM
• Difficulty starting or extended cranking time
• Reduced engine power or poor acceleration
• Engine stalls or misfires, especially when cold
• Increased fuel consumption
• Failed emissions test (in some cases)

Probable Causes for Code P0390 #

The most common triggers for the P0390 code are electrical in nature, but mechanical issues can also play a role. It’s essential to diagnose these causes in order of likelihood, starting with the most common:

1. Faulty camshaft position sensor “B” (exhaust side)
2. Damaged, corroded, or loose wiring/connectors in the sensor circuit
3. Timing chain or timing belt issues causing misalignment
4. Failed ECM (rare), such as an internal circuit fault
5. Oil contamination on the sensor or connector
6. Shorts or opens in the harness (especially after recent engine work)

Step-by-Step Diagnosis for Code P0390 #

Diagnosing P0390 may seem daunting, but a systematic approach makes it manageable. Start by verifying the code and inspecting obvious issues before moving to more advanced tests. Here’s a reliable workflow:

• Step 1: Confirm P0390 with an OBD-II scanner. Check for related codes (especially P0340, P0365, P0014, P0017).
• Step 2: Visually inspect the camshaft position sensor “B” and its wiring for signs of damage, corrosion, or oil intrusion.
• Step 3: Check the sensor connector for tightness and clean contacts.
• Step 4: Test the sensor’s resistance with a digital multimeter. Compare readings to OEM specifications.
• Step 5: Backprobe the sensor circuit for proper voltage supply and signal using a wiring diagram.
• Step 6: Examine the timing chain/belt for wear, slack, or skipped teeth if mechanical timing is suspect.
• Step 7: If all else checks out, consider ECM diagnostics or consult an OEM service manual for advanced troubleshooting.

Possible Repairs for Code P0390 #

Once the root cause is identified, the fix is usually straightforward. Address each underlying issue with the appropriate repair:

• Replace the camshaft position sensor “B” if it’s faulty or not within OEM specs.
• Repair or replace damaged wiring or connectors in the sensor circuit.
• Clean any oil contamination from the sensor or connector.
• Correct timing chain/belt alignment or replace if worn or stretched.
• Update or reprogram the ECM if an internal fault is confirmed (rare).

Is It Safe to Drive with Code P0390? #

Limited use only. While your vehicle may still run with P0390 present, it’s not wise to ignore the code for long. In some cases, drivability is only mildly affected and you can drive short distances to reach a repair facility. However, extended driving risks stalling, rough running, further engine damage, or increased emissions. If you experience significant loss of power or the engine stalls, stop driving and arrange for repairs as soon as possible.

Vehicles Most Commonly Affected by Code P0390 #

P0390 can appear in any OBD-II equipped vehicle, but some models are more prone due to sensor placement or known wiring vulnerabilities. You’re most likely to encounter this code on these vehicles:

• Ford F-150, Explorer, Fusion (2010s)
• Toyota Camry, Corolla, RAV4 (2007–2018)
• Honda Accord, Civic, CR-V (2008–2017)
• Nissan Altima, Sentra, Rogue (2007–2016)
• Hyundai Sonata, Elantra, Santa Fe (2011–2019)
• Kia Optima, Sorento (2012–2018)
• GM Silverado, Malibu, Equinox (2010–2017)
• Chrysler 300, Dodge Charger, Jeep Grand Cherokee (2011–2020)
• Subaru Outback, Forester (2010–2018)

Common Mistakes & Best Practices for P0390 #

Misdiagnosing P0390 is surprisingly common, especially if you skip basic checks or rely only on code readers. To avoid unnecessary expenses and get your vehicle back on track, keep these tips in mind:

• Don’t replace the sensor before checking the wiring. Many issues are due to corroded or damaged connectors, not the sensor itself.
• Avoid clearing codes before diagnosis. You’ll lose valuable freeze-frame data that helps pinpoint the issue.
• Always inspect for oil leaks. Oil contamination can cause false sensor readings and recurring codes.
• Follow OEM wiring diagrams and specs. Do not guess at wire colors or pin positions.
• If in doubt, consult a professional — especially if timing components or ECM faults are suspected.

Quick FAQ for Code P0390 #

Having trouble wrapping your head around P0390? Here are quick answers to the most common questions:

• Q: Can I just clear the code and keep driving?
  A: You can clear it, but if the problem isn’t fixed, the code will return. Ignoring it can lead to worsening engine performance or future damage.
• Q: Is P0390 the same as P0340?
  A: No. P0340 generally refers to the intake camshaft position sensor “A”, while P0390 concerns the exhaust camshaft position sensor “B”. Both can cause similar symptoms, but affect different engine functions.
• Q: Can a bad oil change cause this code?
  A: If excessive oil spills onto the sensor or its wiring, yes, this can trigger P0390 due to contamination or poor connections.