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P codepowertrainMedium severity

P0327Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor)

The Bank 1 (or single) knock sensor circuit is reading below its minimum expected voltage, indicating a shorted or dead sensor circuit.

Definition

The PCM applies a bias voltage to the knock sensor circuit and monitors it; P0327 sets when the Bank 1 sensor input stays below the low threshold, which points to a short to ground, an open sensor element, or a corroded circuit. With no trustworthy knock signal, the PCM defaults to retarded ignition timing, producing noticeably soft acceleration and reduced fuel economy along with an illuminated MIL. This code is especially common on engines whose knock sensors sit in the engine valley under the intake manifold, where coolant leaks or condensation corrode the sensors and connectors.

Common causes

  • Failed knock sensor (open or shorted piezo element)
  • Signal wire shorted to ground or an open in the harness
  • Corroded sensor or connector from water/coolant intrusion (valley-mounted sensors especially)
  • Damaged shielded cable or broken shield drain wire
  • PCM bias/input circuit fault (rare)

Common misdiagnoses

  • Sensor replaced without fixing the water intrusion or wiring short that killed it
  • Ignition components replaced for the retarded-timing power loss
  • PCM replaced when the harness is shorted to ground
  • Engine mechanical work performed for a purely electrical circuit code

Troubleshooting steps

  1. 1.Measure the bias voltage at the sensor connector

    With the connector unplugged and key on, many systems show roughly 2-2.5 V bias on the signal terminal; near 0 V means a harness short to ground or a PCM fault.

  2. 2.Check sensor resistance

    Compare the sensor's resistance to specification (varies widely by design — some read ~100 kΩ, others near-infinite); a shorted element reads near 0 Ω.

  3. 3.Inspect for water or coolant intrusion

    On valley-mounted sensors (common on GM V8s), pull the intake covers and look for standing coolant around the sensors and green corrosion in the connectors.

  4. 4.Isolate the harness

    With sensor and PCM disconnected, verify the signal wire has continuity end to end and infinite resistance to ground; repair any chafe against the block or manifold.

  5. 5.Tap-test after repairs

    Scope the input while tapping the block near the sensor — a clean AC burst confirms the circuit; clear the code and verify timing advance returns to normal on a drive.

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