P2318: Understanding the coil G off-state low-voltage check

For P2318, both the generic label and this GM row identify ignition coil G. The monitor looks for a low voltage while the primary low-side driver is off. The source associates that condition with a short to ground, rather than with a low secondary spark-voltage measurement.

Why a running capture matters

The documented check requires synchronized ignition, more than nine ignition-counter increments and engine speed above 1,400 rpm. Those prerequisites explain why an apparently quiet electrical signal at rest is not equivalent to a successful monitored firing sequence. The fault must satisfy a 0.4-second interval; the reporting designation is two-trip.

Use the fault class to choose the question

The first question is whether the output remains low during the interval in which the controller expects its off-state behavior. A low value during a commanded on period addresses a different condition and cannot by itself verify P2318. Record the command and feedback on the same time basis.

Although the letter agrees here, the document does not supply a universal cylinder-number mapping. Resolve that mapping for the actual engine before touching components. The code describes an electrical failure class, and the table does not determine which connected component or circuit segment caused it.

Document scope and source

2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred. These figures explain the cited controller logic, not a vehicle-specific repair instruction. Match the vehicle’s service information before applying them.

GM physical PDF page 702.