P0328: High knock-sensor DC bias is different from strong knock

The cited GM P0328 monitor evaluates a high electrical bias level on the Bank 1 knock-sensor input or return. It uses a three-resistor network to establish a normal DC diagnostic range and compares the result with the five-volt reference.

A circuit percentage, not knock intensity

The published boundary is above 39 percent of reference. That value describes the diagnostic bias network, not the amplitude of an actual knock event. P0328 therefore should not be translated directly into severe detonation or used to select fuel-related remedies without further evidence.

Either the input line or the return line can satisfy the high condition. Capture both where the approved diagnostic system permits, rather than assuming the fault must lie on one conductor.

Counted evidence and confirmation

With engine speed above zero and below 8,500 rpm, the monitor evaluates 50 failures out of 63 samples at 100 milliseconds per sample. It is Type A, one-trip. A current normal reading does not prove that the earlier bias excursion never occurred.

Use the vehicle-specific circuit procedure to determine what holds the relevant line above its permitted bias range. The source does not independently identify a sensor, connection or controller as the cause. Verification should include a completed passing high-range check, with the correct reference and return context, rather than an observation that the engine sounds normal.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 264. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.