What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II (Dodge, Ram, Ford, GMC, Chevrolet, VW, Toyota, etc.). Although generic, specific repair steps may vary by make/model.
A P033C fault code means the Powertrain Control Module (PCM) has detected a lower than expected sensor reading from the #4 knock sensor on bank 2. Bank 2 is always the engine cylinder bank that does not contain cylinder #1. Refer to a vehicle-specific repair source to determine which sensor is the #4 knock sensor.
Typically threaded directly into the engine block, the knock sensor is a piezoelectric sensor. The location of sensors in a multi-sensor system may vary by manufacturer, but most are located on the sides of the block (between the cylinder liner freeze plugs). Knock sensors located on the sides of the engine block are often screwed directly into the engine coolant passages. When the engine is hot and the engine cooling system is pressurized, removing these sensors can result in severe burns from hot coolant. Before removing a knock sensor, allow the engine to cool and always dispose of coolant properly.
A piezoelectric sensing crystal is at the heart of the knock sensor. When shaken or vibrated, the piezoelectric crystal produces a small amount of voltage. Since the knock sensor control circuit is normally a single-wire ground circuit, the voltage generated by vibration is recognized by the PCM as engine noise or vibration. The severity of the vibration encountered by the piezoelectric crystal (inside the knock sensor) determines the voltage level produced in the circuit.
If the PCM detects a degree of voltage from the knock sensor indicating spark knock; it may retard ignition timing and no knock sensor control code may be recorded. If the PCM detects a voltage level from the knock sensor that indicates more severe engine noise (such as a connecting rod contacting the inside of the engine block), it may interrupt fuel delivery and ignition spark to the affected cylinder and a knock sensor code will be stored.
Code Severity and Symptoms
A stored P033C code should be considered severe as it could indicate internal engine failure.
Symptoms of this code may include:
Hesitation during acceleration
Below normal engine performance
Abnormal noises from the engine area
Increased fuel consumption
Causes
Possible causes for this code being set are:
Ignition misfires
Faulty knock sensor
Internal engine problem
Use of contaminated or low-quality fuel
Faulty knock sensor control wiring and/or connectors
Incorrect PCM or PCM programming error
Diagnostic and Repair Procedures
To diagnose a P033C code, a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle-specific repair resource will be needed. If the engine seems to be knocking or excessively noisy, address this issue before attempting diagnosis for any knock sensor code.
Check Technical Service Bulletins (TSBs) that may apply to your year/make/model. If the problem is known, there may be a bulletin providing specific diagnostic and repair assistance for your exact issue. This can save you time and money.
Start with a visual inspection of all wiring harnesses and connectors related to the system. Look for corroded, burned, or otherwise damaged wires and connectors that could create an open or short circuit. Knock sensors are often located in the lower part of the engine block. This makes them susceptible to damage when heavy parts (like starters and motor mounts) are replaced. System connectors, wiring, and fragile knock sensors are frequently broken during nearby repairs.
Connect the OBD-II scanner to the vehicle’s diagnostic connector and retrieve all stored diagnostic trouble codes and freeze frame data. Note this information for use in the diagnostic process. Clear the codes and test-drive the vehicle to see if they reset.
If the P033C resets, start the engine and use the scanner to observe the knock sensor data. If the scanner indicates that the knock sensor voltage is not within manufacturer specifications, use the DVOM to test the live data at the knock sensor connector. If the signal at the connector is within specifications, suspect a wiring problem between the sensor and the PCM. If the voltage at the knock sensor connector is not within specifications, suspect a faulty knock sensor. If replacing the sensor is the next step, ensure you do not come into contact with hot coolant. Wait for the engine to cool before removing the old sensor.