P0366: Bank 1 camshaft Sensor B pulse-count plausibility

P0366 is the performance diagnostic for Bank 1 camshaft Sensor B in this GM section. The controller compares the number of cam pulses with crank-referenced observation windows. A waveform can be present and still fail because pulses are missing or additional edges are counted.

Short and long windows answer different questions

At startup, a twelve-event medium-resolution crank window fails below four or above six cam pulses. A second method examines 100 engine cycles and fails below 398 or above 402 pulses. The startup test begins at crank region 3; its eligibility begins with starter engagement and can continue after the starter releases.

Both paths require crankshaft synchronization and no relevant crank-sensor fault. An unreliable crank reference changes the meaning of the apparent cam count and must be considered first.

Evidence beyond a live angle display

Capture the number and placement of cam edges against the correct crank pattern using the vehicle's approved procedure. A scan value reporting a plausible cam angle does not prove that every required pulse was received throughout the monitor window.

The page does not determine whether signal integrity, the sensor or the target explains a failed count. Confirm the specific engine's expected pattern before assigning a mechanical cause. Verification should show passing counts in the affected startup or continuous window with the reference synchronized, rather than only clearing P0366 and checking for an immediate return.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 275. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.