P0331: A high knock reference is different from a low circuit fault

P0331 is a performance or rationality code for knock sensor B. The GM row evaluates the normalized reference level used by knock control, rather than the low electrical-output condition associated with a short-to-ground check.

The reference has its own units and history

The boundary is calibration-dependent, listed between 0.67109 and 2.5 volt-milliseconds with a lookup-table reference. It is not a fixed voltage that can be checked at a connector with an ordinary instantaneous reading.

A debounce counter above 30 counts accompanies the comparison. The table lists a 0.1-second evaluation interval and two-trip reporting, but those labels should not erase the accumulated-counter requirement.

The operating state must match

Coolant temperature at engine start must exceed 34.96°C and knock control must be active. Load, dynamic behavior and other release conditions further qualify the assessment. A reference level recorded while knock control is inactive cannot be judged as if it came from the eligible monitor window.

For a useful diagnostic record, retain the sensor 2 identification, normalized reference value and control-status context. The source does not equate a high reference result with a confirmed damaged engine or a defective knock sensor. Its value is in separating a reference-plausibility issue from basic electrical range faults, so that the applicable service procedure can investigate the correct path.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 603; GM diagnostic table, PDF page 604.