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P0391 is a diagnostic trouble code (DTC) for "Camshaft Position Sensor "B" Circuit Range/Performance (Bank 2)". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $154.99 . Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $50.0 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
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This is the generic OBD-II code for Camshaft Position Sensor "B" Circuit Range/Performance (Bank 2). Sensor B typically refers to the exhaust camshaft side, while Bank 2 indicates that the problem is on the side of the engine which does not contain cylinder #1.
The camshaft position sensor tells the Powertrain Control Module (PCM) what position the camshaft is in, in order to facilitate proper fuel delivery and ignition timing. The sensor sends a signal to the PCM in the form of a voltage reading. If this reading deviates from the expected specifications, the computer detects that the camshaft position is abnormal, and Diagnostic Trouble Code (DTC) P0391 will set.
Possible causes of this DTC include:
Due to the fact that the camshaft position dictates fuel injection and cylinder firing timing, you may notice sluggish acceleration, poor engine performance, or rough engine idling. The vehicle may refuse to start at all, and the Check Engine or Service Engine Soon light may illuminate.
Diagnosing P0391 may require:
Verifying any existing Diagnostic Trouble Codes using a scanner and recording relevant data, such as the order in which the codes occurred
Clearing all codes and road testing the vehicle above 45mph in order to see if the codes return
Diagnosing and repairing any errors which occurred prior to the camshaft sensor circuit problem
Visually inspecting the relevant wiring and connectors to check for corrosion, shorts, opens, or loose connections
Visually inspecting the circuitry for signs of engine oil or other fluids which may have spilled over, causing damage to the sensor or wiring
Testing the resistance and voltage of the camshaft position sensor and connector
Testing system continuity using a digital volt/ohmmeter
Keep in mind that some vehicles will set a camshaft sensor code when there is a faulty crankshaft sensor, so you may need to look into that possibility if none of the above diagnoses pan out.
Frequent errors include automatically assuming the sensor is the problem, rather than examining and replacing any faulty wiring or connectors. In addition, if a circuitry problem is being cause by a leak, replacing the faulty parts won’t fix the issue. Other malfunctions must be addressed in order to prevent the code from returning.
This DTC should be taken seriously, as the camshaft position sensor has a direct effect on the engine’s function. Engine performance may be affected, resulting in driving conditions which are both unpleasant and unsafe. In addition, if the issue isn’t resolved promptly, other components could be affected and sustain damage.
Fixing this DTC may involve:
There are some cases in which aftermarket parts are sufficient, however experts recommend only using OEM parts when replacing sensors. Even though they may be more expensive, they experience failure much less frequently than non-OEM sensors, which saves you time, money, and hassle in the long run.
If you’re doing repairs to the camshaft sensor or related components, it’s best to replace both the camshaft and crankshaft versions at the same time, rather than individually. This ensures that they wear at the same rate, thus avoiding having to continually switch off replacing one or the other.
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