P06B6: the knock-monitor test circuit has its own diagnostic

P06B6 checks an internal circuit used by the knock-sensor 1 open-circuit diagnostic in the cited GM implementation. The source specifically limits this check to the diagnostic method using a 20 kHz signal component.

A fault in the test is not proof of engine knock

The controller examines the 20 kHz range of an FFT output and declares the internal test-circuit fault when that signal lies between calibrated minimum and maximum thresholds. Those thresholds are in supporting tables, not numeric values in the supplied row. This article therefore does not invent a sensor voltage or knock-intensity limit.

The monitor is assessing the integrity of its diagnostic mechanism. It does not itself establish damaging combustion knock or prove that the external knock sensor is open.

Operation must qualify the test

The listed prerequisites include more than two seconds of engine run time, speed above 680 and below 4,500 rpm, and more than 125 accumulated revolutions within that speed window per key cycle. Airflow must also fall within the stated range. A short idle observation immediately after startup may not complete these prerequisites.

The result uses a first-order lag filter updated each engine event. That means event history matters more than one instantaneous reading. Verification should confirm the internal diagnostic passes after qualifying operation using the exact service procedure. The source supplies no basis for replacing a knock sensor solely from this processor-performance code.

Source and applicability

Documented monitors in gm-2025-03a, model year 2025. These are module/calibration examples; vehicle, engine and transmission applicability must be confirmed independently. GM 2025-03a, page 426.