P033A: Knock-sensor D circuit evidence needs a channel-label check

P033A is cataloged as knock-sensor D circuit. The GM summary row describes an open-load monitor but names sensor 3, a label also used elsewhere for the C-channel codes. The relationship between those internal and generic names must be confirmed before identifying physical hardware.

The documented open-load strategy remains useful

The controller integrates diagnostic evidence and uses a 30-event qualification with two-trip reporting. The check runs at intervals of 15–120 seconds depending on speed. These features make monitor-completion information more useful than a single measurement taken immediately after clearing faults.

Eligibility includes sensor PWM duty above 50 percent, engine speed from above 800 to below 5,000 rpm, and load from above 13 to below 160 percent. The short-to-ground and short-to-battery diagnostic functions must be enabled.

Do not guess the sensor location

The source’s sensor-3 wording is not silently changed to sensor 4. Confirm the installed calibration’s P033A mapping through the proper service information before following a harness branch. A generic letter designation alone cannot establish that mapping.

The integrated result is an internal open-load metric, not a published resistance specification. The monitor supports investigation of circuit continuity under qualified conditions, but it does not locate an interruption or prove a particular sensor failed. Keep the unresolved channel label separate from the otherwise documented detection principle when deciding the next diagnostic step.

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 605; GM diagnostic table, PDF page 606.