Engine

P033C — Knock Sensor 4 Circuit Low (Bank 2)

Severity: medium Drive with care, to a shop

What P033C means

The engine control module detected that the signal from knock sensor 4 on bank 2 is below the expected range. Knock sensors bolt to the engine block and listen for the vibration pattern of detonation. The module uses them to pull back spark timing when knock occurs. A low signal means knock protection may be inaccurate or disabled.

Symptoms

  • Check Engine light on
  • Reduced power or sluggish acceleration
  • Worse fuel economy
  • Possible pinging or knocking under load
  • Rough running when the engine is working hard

Possible causes

  1. Failed knock sensor 4 on bank 2
  2. Open, shorted or corroded wiring in the sensor circuit
  3. Corroded or loose sensor connector
  4. Poor ground or shield connection in the circuit
  5. Sensor loose or improperly torqued (less common)
  6. Internal PCM input fault (rare)

How to diagnose

  1. Scan all codes and freeze frame data, then clear the code and see if it returns
  2. Find knock sensor 4 on bank 2 using the engine's service information and inspect it and its wiring
  3. Check the connector for corrosion, moisture and bent or backed-out terminals
  4. Test the harness for opens and shorts to ground or power between sensor and PCM
  5. Check sensor resistance or signal per specifications, and watch scan tool data while tapping the block near the sensor
  6. Verify the sensor's mounting surface and torque
  7. If wiring and sensor test good, check PCM power and grounds before suspecting the PCM

Common fixes

  • Replace knock sensor 4 on bank 2 and torque it correctly
  • Repair or replace damaged wiring and connectors
  • Clean and restore ground and shield connections
  • Reprogram or replace the PCM only if it is confirmed faulty

Questions and answers

What does P033C mean?

It means the signal in the knock sensor 4 circuit on bank 2 is too low. The PCM can't reliably detect knock and may retard timing as a precaution.

Can I drive with P033C?

Briefly and gently, yes, but get it checked soon. Without knock protection the engine can be damaged, especially with low-quality fuel or heavy load.

Do I always need a new knock sensor?

No. Wiring and connector faults are common, so inspect and test the circuit before replacing the sensor.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.