P0325

P0325 indicates a general circuit fault on knock sensor 1 (bank 1) - the PCM is not seeing a usable signal at all. The cheapest-first ladder depends on sensor type. Piezo-flat-washer sensors (Toyota, Honda, most modern Asian engines) should show roughly 4 to 5 megohms across the sensor terminals with the connector unplugged. Resonant tuned sensors (most GM LS, older Ford) typically read about 90 to 110 kohm. With the sensor connected and engine running, backprobe the signal wire to ground with an AC-coupled scope or DMM on AC volts - a healthy piezo sensor produces about 20 mV to several hundred mV AC during normal combustion noise, with sharp spikes during a tap on the engine block near the sensor. Verify the shield/ground side is intact, since knock sensors are typically a shielded twisted pair. Caveat: never condemn a knock sensor on a GM LS truck (4.8/5.3/6.0) without first inspecting the under-intake engine harness - this is the #1 misdiagnosis in GM truck shops and the actual fault is harness corrosion, not the sensor.

Vehicle-specific patterns: 1999-2007 GM Silverado/Sierra/Tahoe/Yukon/Suburban 4.8/5.3/6.0 LS is the epidemic platform - knock sensors live in the lifter valley UNDER the intake manifold and the foam mat traps moisture against the harness, corroding the connectors and pigtails. GM TSB 02-06-04-037 covers the harness replacement. 2003-2008 Honda Accord/Element/CR-V K24 has a known knock sensor internal failure around 100k-150k miles. 2005-2009 VW/Audi 2.0T (BPY) suffers chafed knock sensor harness against the cylinder block. 2007-2013 BMW N52/N54 sets P0325 from cracked knock sensor connectors under the intake. Estimated repair: $80 to $700.