Technical Description of OBD-II Trouble Code
Range/Performance Issue with Camshaft Position Sensor “B” in Bank 2
What does that signify?
This is a generic diagnostic trouble code (DTC) for the powertrain, applicable to all makes and models manufactured from 1996 onwards. The specific troubleshooting steps may vary depending on the vehicle.
The P0391 code indicates that the powertrain control module (PCM) has detected a problem with the camshaft signal “B” in bank 2. Bank 2 refers to the set of cylinders in the engine that does not include cylinder #1.
Description and correlation of the crankshaft and camshaft position sensors
Understanding the function and interaction of these sensors is crucial in modern vehicles. In distributorless ignition systems, a crank and cam sensor are used instead of an electronic distributor and trigger wheel.
The crankshaft position sensor (CPS) informs the engine control module about the position of the pistons relative to top dead center, enabling fuel injection and spark plug ignition. The camshaft position sensor (CMP) indicates the position of the camshaft intake lobe in relation to the CPS signal, facilitating fuel injection in each cylinder.
Description and location of sensors
Both the crank and cam sensors generate an “on and off” signal, functioning either through hall effect or magnetism.
A hall effect sensor utilizes an electromagnetic sensor and a reluctor. The reluctor resembles a picket fence with small cups and square cutouts on the sides. While the reluctor rotates, the sensor remains stationary and positioned closely to it. Each time a post passes in front of the sensor, a signal is produced, and the signal turns off when the post passes.
A magnetic pickup consists of a stationary sensor and a magnet attached to the rotating component. Whenever the magnet passes in front of the sensor, a signal is generated.
Locations
A hall effect crank sensor is typically located on the harmonic balancer at the front of the engine. The magnetic pickup can be found on the side of the engine block, utilizing the center of the crankshaft as a signal source, or in the bellhousing, using the flywheel as a trigger. The camshaft sensor is mounted either at the front or rear of the camshaft. In the case of P0391, it specifically pertains to bank 2, which does not include cylinder #1.
Symptoms
The vehicle will likely continue to run with this code, as it is often intermittent. Additionally, the PCM can often operate the vehicle in “limp-in/limp-home” mode even with a cam sensor signal issue. There may be no noticeable symptoms other than:
Causes
A code P0391 may indicate one or more of the following:
Possible Solutions
It is always advisable to start by searching for any relevant technical service bulletins (TSBs) specific to your vehicle. The vehicle manufacturer may have a PCM flash or reprogram available to address this issue, so it is worth checking before pursuing other avenues.
Here are some steps to consider:
Related Camshaft Trouble Codes: P0340, P0341, P0342, P0343, P0345, P0346, P0347, P0348, P0349, P0365, P0366, P0367, P0368, P0369, P0390, P0392, P0393, P0394.
