What does it mean?
OBD II fault code P0370 is a generic code that is defined as “Timing reference, high resolution signal A – malfunction”, and is set when the PCM (Powertrain Control Module) fails to detect a timing reference signal. Note that while this code primarily refers to a problem in an engine position sensor (aka crankshaft position sensor) circuit, failure of engine position sensors can also cause this code to set.
In order for the PCM on any modern application to control and monitor engine speed, fuel injection strategies, ignition timing, (fuel injection timing on diesels), and misfire diagnostics effectively, it requires a timing reference signal that tells the PCM where the crankshaft (and hence the #1 piston) is during a crankshaft rotation. In other words, the PCM needs to know how many degrees of rotation the crankshaft has completed during a rotation, relative to a fixed starting point.
In a fully functional system, the generated signal is delivered to the PCM via a dedicated signal circuit, or a varying resistance in the case of two-wire sensors. In practice, this timing reference signal is generated by a sensor whose magnetic field is interrupted by the teeth on a reluctor wheel that (depending on the application) can be located on the crankshaft pulley (aka harmonic balancer), a camshaft, flywheel or flex plate, or inside the fuel pump on some diesel applications.
Refer to the Trouble Shooting section of this guide for more details on the types of engine position sensors in use today. The image below shows the typical arrangement of an engine position sensor and its reluctor ring, which in this case, is located on the harmonic balancer. Note that while this particular example is adjustable by means of the slotted mounting slots, most engine position sensors are not adjustable.