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P codepowertrainMedium severity

P033EKnock Sensor 4 Circuit Intermittent (Bank 2)

The PCM detected an intermittent or erratic signal from the knock sensor 4 circuit on bank 2.

Definition

P033E sets when the knock sensor 4 signal repeatedly drops out or spikes and then recovers, rather than failing solidly — behavior the PCM classifies as intermittent and which almost always traces to a connection or harness problem. Each time the fault is active the PCM suspends knock control for those cylinders and retards timing defensively, so the MIL illuminates and the driver may notice inconsistent performance and reduced fuel economy. Because the fault comes and goes, it can be present in history with the circuit testing fine in the bay, making wiggle testing essential.

Common causes

  • Loose or corroded connector terminals making intermittent contact
  • Chafed harness insulation touching ground only under engine movement or vibration
  • Knock sensor with an internal intermittent open (often temperature-dependent)
  • Sensor working loose from its mounting boss
  • EMI from failing ignition components inducing noise into the circuit
  • Damaged shield drain wire on the sensor cable

Common misdiagnoses

  • Replacing the sensor when a connector terminal has lost tension
  • Replacing the PCM
  • Clearing the code without diagnosis because the circuit currently tests good
  • Replacing coils for a perceived intermittent misfire

Troubleshooting steps

  1. 1.Pull freeze-frame data

    Note temperature, RPM, and load when the code set — heat-related intermittents often only appear fully warmed up.

  2. 2.Wiggle-test with live data displayed

    Flex the harness and connector while watching the knock sensor PID or pending-code status; a glitch during manipulation localizes the fault.

  3. 3.Inspect terminal tension and condition

    Remove the connector and check for spread female terminals, green corrosion, and oil wicking down the wires into the cavity.

  4. 4.Check sensor mounting

    Verify the sensor is torqued to spec on a clean boss; a loose sensor produces an erratic, chattering signal.

  5. 5.Monitor with a scope over a test drive

    Record the sensor circuit during a drive replicating freeze-frame conditions and look for momentary dropouts to full bias or to ground.

  6. 6.Repair and verify over multiple drive cycles

    Because the fault is intermittent, confirm the fix across several warm-up and load cycles before returning the vehicle.

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