P033C

What it means

P033C is the generic code for a low signal in the circuit of knock or combustion vibration sensor D. The engine control unit saw the sensor's signal voltage fall below the expected range, which suggests a short to ground, an open or damaged circuit, or a failed sensor. Which cylinder bank or position 'D' refers to depends on the model and engine, so check the manufacturer's data.

Symptoms

• Engine warning light on
• Reduced power or sluggish acceleration
• Retarded ignition timing causing poorer fuel economy
• Pinking or rough running under load
• Hesitation when accelerating

Possible causes

• Damaged, chafed or corroded wiring to the knock sensor, including a short to groundlikely
• Poor connection or water ingress at the knock sensor connectorlikely
• Faulty knock or combustion vibration sensorlikely
• Sensor loose or incorrectly torqued, giving a poor signalpossible
• Open circuit or short in the sensor reference or shield wiringpossible
• Fault in the engine control unitrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, such as engine load, speed and temperature, at the time of setting.
2. Check the manufacturer's data to identify which sensor is D on this engine and where it is fitted.
3. Inspect the sensor wiring and connector for chafing, heat damage, oil contamination, corrosion and water.
4. Check the sensor is fitted correctly, with the right mounting surface and tightening torque.
5. Measure the sensor circuit for a short to ground, open circuit and resistance against the manufacturer's specification.
6. Check the supply, reference and signal voltages at the control unit connector as specified for the model.
7. Check live data with the engine running to see whether the sensor signal responds, and clear the code to see if it returns.
8. If the wiring and sensor test fine, check for software updates and consider the control unit only after everything else has been ruled out.

How to fix

• Repair or replace damaged wiring and fix any short to ground.
• Clean, dry and refit the connector, or replace it if the terminals are corroded or damaged.
• Replace the faulty knock sensor and tighten it to the specified torque.
• Correct a loose or badly seated sensor installation.
• Apply a calibration update only if the manufacturer lists it as a known cause for this code on the vehicle.
• Repair or replace the control unit if it is confirmed faulty.

Can I keep driving?

Nearby codes

• P033BGenericKnock/Combustion Vibration Sensor D Circuit Range/Performance
• P033DGenericKnock/Combustion Vibration Sensor D Circuit High