P0326

P0326 means the knock sensor signal is present but its amplitude or frequency profile is outside the expected window - it sees the sensor electrically but the noise floor is wrong. The cheapest-first diagnostic is a controlled tap test: with the scan tool graphing knock sensor counts or KR (knock retard) live, lightly tap the engine block within 6 inches of the sensor with a small wrench. A healthy sensor produces immediate, sharp spikes. No response means a dead or detached sensor; constant high noise even at idle means a cracked sensor or a torque problem (most knock sensors require a specific torque, typically 15-22 ft-lb, to couple properly to the block). Verify resistance against type: piezo flat-washer about 4-5 megohms, resonant about 90-110 kohm. Inspect for any contact between the sensor body and a harness, bracket, or coolant line that would inject mechanical noise. Caveat: aftermarket knock sensors frequently have wrong resonant frequency for the PCM calibration and will set P0326 even though they pass a bench test.

Vehicle-specific patterns: 1999-2007 GM 4.8/5.3/6.0 LS trucks routinely set P0326 from the same under-intake harness corrosion that causes P0325/P0327 - the signal makes it through but is degraded. 2003-2008 Honda Accord/CR-V K24 K-series engines set P0326 when the knock sensor cracks internally after long heat cycling. 2006-2012 Audi/VW 2.0T FSI (BPY, CCTA) sets P0326 from chafed harness on the engine block. 2005-2008 Subaru Legacy/Outback 2.5L turbo has a TSB for incorrect knock sensor torque from the factory. Estimated repair: $80 to $700.