What does it mean?
OBD fault code P0371 is defined as “Timing Reference High Resolution Signal “A” – Too Many Pulses”, and can be set either when the Crank Position Sensor, also sometimes known as the Crank Angle Sensor fails, or when something interferes with, or changes the pattern and /or arrangement of the reluctor ring that works in conjunction with the sensor, thereby causing too many ignition/fuel injection pulses to be generated.
Crank Position Sensors come in two types; one type that has only two wires leading out of it, and a second type that has three wires. This is important to remember during testing, since the two-wire type produces am analog signal that can only be tested in AC Volts, while the three-wire type, known as Hall-effect sensors, produce a digital DC Volt signal that can only be tested in DC Volts, or in Hertz Frequency mode.
One of the wires on three-wire type sensors supply the sensor with power(which two-wire types do not have), that can be either 9-, or 12 Volts. The section on troubleshooting provides more info on what each wire does. Both types of Crank Position Sensor work by generating a magnetic field that is interrupted by the reluctor ring the sensor is mounted close to.
The interruption of the magnetic field is what generates the signal that is used to generate an ignition spark, as well as a signal to the ECU to activate the fuel injection system. All reluctor rings on all engines have a gap that spans the width of two teeth that serves as a reference to indicate when cylinder #1 is at top dead centre. This reference serves as the basis for all other signals that regulate the smooth and efficient operation of the engine.
The image above shows a typical Crank Position Sensor, and its position relative to the reluctor ring that works in conjunction with it. Note that the reluctor ring is not always located outside the engine, as it is on this Ford engine. In many cases, especially on GM products, the wheel is located inside the crank case and can only be accessed by removing the oil pan, although the Crank Position Sensor itself may be accessible from outside the engine.
Also note the small air gap between the sensor and the teeth on the wheel; this gap is crucial to the correct functioning of the sensor. In this particular application, the sensor is capable of some adjustment by virtue of the slotted mounting holes. Moving the sensor upward in the direction of the engine’s rotation will retard the ignition timing, while moving it downward against the engine’s rotation will advance the timing.