Fix P0391: STEP-BY-STEP diagnostic GUIDE!

The P0391: Camshaft Position Sensor ‘B’ Circuit Range/Performance (Bank 2) code indicates that the engine control module (ECM) has detected an issue with the signal range or performance from camshaft position sensor B on bank 2. This sensor plays a critical role in managing engine timing and fuel injection by monitoring the camshaft’s position. A malfunction in this sensor’s circuit can cause poor engine performance, misfires, or timing issues.

P0391 – Quick Overview

Meaning	P0391: Camshaft Position Sensor ‘B’ Circuit Range/Performance (Bank 2)
Is it serious?	Yes, this code can cause timing issues, misfires, poor engine performance, or even failure to start.
Possible causes	– Faulty camshaft position sensor – Incorrect sensor gap or alignment – Timing chain/belt issues
How to diagnose?	– Test the camshaft position sensor range – Verify sensor gap and alignment – Inspect timing chain or belt for wear

P0391 Meaning

The P0391: Camshaft Position Sensor ‘B’ Circuit Range/Performance (Bank 2) code means that the ECM is receiving an out-of-range or incorrect signal from camshaft position sensor B on bank 2. This signal is essential for accurate engine timing. Problems with the sensor, incorrect alignment, or timing chain/belt issues can disrupt the signal, leading to misfires, rough engine performance, or even stalling.

Step-by-step diagnostic guide

Follow these steps to diagnose and resolve the P0391 code by addressing potential causes one by one.

Action	Description	Tools Needed
Check for Other Codes	Use an OBD-II scanner to check for other related codes that may provide more insight into camshaft position sensor B or other timing-related issues.	OBD-II Scanner
Test the Camshaft Position Sensor Range	Use a multimeter to test the output signal from camshaft position sensor B on bank 2. Compare the results with manufacturer’s specifications to confirm if the sensor is working within range.	Multimeter, Manufacturer’s Specifications
Verify Sensor Gap and Alignment	Ensure that camshaft position sensor B is correctly aligned and has the proper gap between the sensor and the camshaft. An incorrect gap can lead to performance issues. Adjust the gap if necessary.	Feeler Gauge, Manufacturer’s Specifications
Inspect Timing Chain or Belt for Wear	Check the timing chain or belt for signs of wear, stretching, or misalignment. A worn or damaged timing chain/belt can disrupt the camshaft’s signal, leading to performance issues. Replace if necessary.	Timing Light, Flashlight, Replacement Timing Components
Replace Faulty Components	If the camshaft position sensor, wiring, or timing components are faulty, replace the necessary parts to restore normal engine performance.	Replacement Camshaft Position Sensor, Timing Components
Clear the Code and Test Drive	After completing repairs, clear the P0391 code using an OBD-II scanner. Test drive the vehicle to ensure the problem is resolved and the engine runs smoothly.	OBD-II Scanner, Vehicle Owner’s Manual
Recheck for Codes	After the test drive, re-scan the vehicle to confirm that the P0391 code has not returned. If the code reappears, further diagnosis may be required.	OBD-II Scanner

This diagnostic guide will help you resolve the P0391 code, ensuring that camshaft position sensor B and its related components provide accurate signals for proper engine timing and performance, especially on bank 2.