P033C Knock sensor 4 circuit low (bank 2)

OBD-II DTC Datasheet

Low signal level in the knock sensor circuit 4 (Bank 2)

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles (Dodge, Ram, Ford, GMC, Chevrolet, VW, Toyota, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

DTC P033C means the powertrain control module (PCM) has detected a lower than expected knock sensor # 4 reading on block 2. Block 2 is always an engine block that does not contain cylinder # 1. See your car repair technician to determine which sensor is the # 4 knock sensor.

The knock sensor is usually screwed directly into the cylinder block and is a piezoelectric sensor. The location of the sensors in a multi-sensor system may vary from manufacturer to manufacturer, but most are located on the sides of the unit (between the water jacket frost plugs). Knock sensors located on the sides of the cylinder block are often screwed directly into the engine coolant passages. When the engine is warm and the engine cooling system is pressurized, removal of these sensors can cause severe burns from hot coolant. Allow the engine to cool before removing the knock sensor and always dispose of the coolant properly.

The knock sensor is based on a piezoelectric sensitive crystal. When shaken or vibrated, the piezoelectric crystal creates a small voltage. Since the knock sensor control circuit is usually a single-wire ground circuit, the voltage generated by the vibration is recognized by the PCM as engine noise or vibration. The vibration force that the piezoelectric crystal (inside the knock sensor) encounters determines the level of voltage created in the circuit.

If the PCM detects a degree of knock sensor voltage indicative of spark knock; this may slow down the ignition timing and the knock sensor control code cannot be stored. If the PCM detects a knock sensor voltage level that indicates a louder engine noise (such as a connecting rod contacting the inside of the cylinder block), it may cut off fuel and spark to the affected cylinder and a knock sensor code will appear. stored.

Code severity and symptoms

A stored P033C code should be considered serious as it could indicate an internal engine malfunction.

Symptoms of this code may include:

Oscillation on acceleration
Below normal engine power
Abnormal noises from the engine area
Increased fuel consumption

reasons

Possible reasons for setting this code:

Ignition misfires
Knock sensor defective
Internal engine problem
Contaminated or low-quality fuel used
Faulty knock sensor wiring and / or connectors
Bad PCM or PCM programming error

Diagnostic and repair procedures

Diagnosing a P033C code will require a diagnostic scanner, a digital volt / ohmmeter (DVOM), and a reliable vehicle-specific repair resource. If the engine sounds like it is knocking or is too noisy, troubleshoot the problem before attempting to diagnose any knock sensor codes.

Check out Technical Service Bulletins (TSB) that may be specific to your year / make / model. If the problem is known, there may be a bulletin to help diagnose and fix the specific problem. This will save you time and money.

Begin by visually inspecting all system-related wiring harnesses and connectors. Look for corroded, burnt, or otherwise damaged wiring and connectors that could create an open or short circuit. Knock sensors are often located at the bottom of the cylinder block. This makes them vulnerable to damage when replacing heavy parts (such as starters and engine mounts). System connectors, wiring, and fragile knock sensors often break during repairs nearby.

Connect the OBD-II scanner to the car diagnostic socket and get all stored diagnostic codes and freeze frame data. Record this information for use in the diagnostic process. Clear the codes and test drive the vehicle to see if any are reset.

If P033C is reset, start the engine and use the scanner to monitor the knock sensor data. If the scanner shows that the voltage of the knock sensor is not within the manufacturer's specifications, use the DVOM to check the real-time data at the knock sensor connector. If the signal at the connector is within specification, suspect a wiring problem between the sensor and the PCM. If the voltage at the knock sensor connector is out of specification, suspect that the knock sensor is defective. If the next step is to replace the sensor, make sure you are not in contact with hot coolant. Wait for the engine to cool before removing the old sensor.

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