DTC Code P0391 – What does this code mean?

<ul> <li><b>Malfunction Indicator Lamp (MIL) illumination</b>: The check engine light will illuminate, indicating an issue with the camshaft position sensor B circuit on bank 2. This is a direct result of the PCM detecting a range/performance problem.</li> <li><b>Lack of power</b>: The vehicle may experience reduced power output. This can be caused by the PCM entering 'limp-in/limp-home' mode to protect the engine from potential damage due to the camshaft position sensor issue.</li> <li><b>Possible no start condition</b>: In some cases, the engine may fail to start. This can occur if the PCM is unable to receive a proper signal from the camshaft position sensor B, affecting the timing and fuel injection.</li> <li><b>Stalling</b>: The engine may stall intermittently. This symptom is linked to the PCM's inability to accurately determine the camshaft position, leading to improper engine operation.</li> </ul>

<ul><li>The camshaft position sensor (CMP) 'B' may be faulty, leading to incorrect readings.</li><li>Poor wiring connections at the cam sensor 'B' can cause intermittent or no signal.</li><li>An electrical short or open condition in the associated wiring can disrupt the sensor's performance.</li><li>A low or bad battery can affect the sensor's ability to function correctly.</li></ul>

<ul> <li><b>Initial Inspection</b>: Inspect the wiring and connectors for the Camshaft Position Sensor B on Bank 2. Look for any signs of damage, corrosion, or disconnection.</li> <li><b>Check Sensor Voltage</b>: Using a multimeter, measure the voltage at the sensor connector. Ensure the voltage is within the manufacturer's specified range.</li> <li><b>Test Sensor Resistance</b>: Disconnect the sensor and measure its resistance. Compare the reading to the manufacturer's specifications to determine if the sensor is faulty.</li> <li><b>Inspect Timing Components</b>: Check the timing chain or belt for proper alignment and tension. Misalignment can cause incorrect camshaft position readings.</li> <li><b>Scan for Additional Codes</b>: Use an OBD-II scanner to check for any other related codes that might indicate a broader issue.</li> <li><b>Perform a Live Data Test</b>: Monitor the camshaft position sensor data in real-time using a scan tool. Look for irregularities or inconsistencies in the sensor readings.</li> <li><b>Check Engine Control Module (ECM)</b>: Inspect the ECM for any signs of damage or malfunction. Ensure it is properly receiving and processing signals from the camshaft position sensor.</li> <li><b>Replace Sensor if Necessary</b>: If all tests indicate a faulty sensor, replace the Camshaft Position Sensor B on Bank 2 and clear the code. Re-test to confirm the issue is resolved.</li></ul>

<p>The DTC code P0391 indicates an issue with the Camshaft Position Sensor B Circuit Range/Performance on Bank 2. This is a <b>moderate</b> issue as it can affect engine performance and fuel efficiency.</p><ul><li>Immediate actions: Inspect the wiring and connections to the sensor.</li><li>Potential risks: Delayed repair can lead to poor engine performance, increased fuel consumption, and potential engine stalling.</li></ul>