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P codepowertrainMedium severity

P033DKnock Sensor 4 Circuit High (Bank 2)

The knock sensor 4 circuit on bank 2 is reading a higher voltage than the PCM considers possible.

Definition

The PCM monitors the DC bias level on the knock sensor 4 circuit to verify its integrity; P033D sets when that voltage sticks above the valid window, which points to an open circuit or a short to a voltage source rather than genuine engine noise. Knock control from this sensor is disabled and the PCM falls back to retarded base timing, so expect the MIL, slightly softer performance, and reduced fuel economy. As with all knock sensor faults, real detonation on the affected cylinders goes undetected under load until the circuit is fixed.

Common causes

  • Open in the sensor wiring or connector (broken wire, backed-out or corroded terminal)
  • Knock sensor internally open
  • Signal wire shorted to a power circuit after harness damage
  • Connector left unplugged or not fully latched after engine service
  • PCM input circuit fault (rare)

Common misdiagnoses

  • Replacing the sensor when a valley connector was simply left loose after intake work
  • Replacing the PCM
  • Replacing ignition parts for suspected knock
  • Repairing the wrong bank's sensor due to mislabeled sensor positions

Troubleshooting steps

  1. 1.Verify the connector is seated

    Knock sensor connectors under the intake are frequently left unlatched after service; confirm the lock is engaged and terminals are not backed out.

  2. 2.Measure the circuit voltage

    Compare the backprobed key-on voltage to the bias spec; a reading at or near battery voltage indicates a short to power, while a full-rail bias with no sensor load suggests an open.

  3. 3.Check continuity end to end

    With the sensor and PCM disconnected, verify the signal and return wires each read near 0 Ω; an open confirms a harness break.

  4. 4.Measure sensor resistance

    An OL reading across the sensor terminals (versus the typical ~100 kΩ spec on resistor-type units) condemns the sensor.

  5. 5.Repair, clear, and confirm

    Restore the circuit, verify normal bias voltage, and confirm the code does not return under freeze-frame conditions.

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