P0386: Present but inconsistent low-resolution crank timing

P0386 addresses the performance of the low-resolution crank signal in GM's group 09 timing system. The documented check expects a particular relationship between low-resolution pulses, medium-resolution pulses and a cam event. A signal can be present yet fail that relationship.

Why pulse presence is insufficient

The source distinguishes a low-resolution count other than the expected six, while excluding zero from this performance condition. Zero belongs to the neighboring circuit-loss logic. That separation matters: seeing pulses on diagnostic equipment does not automatically rule out P0386, and complete absence should not be described as the same failure pattern.

The controller requires corroborating medium-resolution and cam information. It also applies a 40-of-50 failure counter under qualified running conditions. A pulse count detached from its reference interval is therefore not an equivalent diagnostic test.

Preserve the pattern and its context

Record which timing references remain valid, whether synchronization changes, and which companion codes are present. Use the specific engine's service procedure to interpret the waveform or controller data; the summary provides no universal sensor gap or wiring-pin test.

The code does not prove whether the inaccurate pattern originates in sensing, wiring or the mechanical reference. Verification needs consistent recognized relationships and completed monitoring under the relevant conditions. Merely clearing memory or confirming that the engine runs briefly leaves the original count disagreement untested.

Source and applicability

2009 General Motors diagnostic parameter file 09OBDG09 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.

GM diagnostic parameters, PDF page 23.