Technical Description of OBD-II Trouble Code
Malfunction in the Circuit of Knock Sensor 4 (Bank 2)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles (Dodge, Ram, Ford, GMC, Chevrolet, VW, Toyota, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
A P033A trouble code indicates that the powertrain control module (PCM) has detected an unexpected sensor reading from knock sensor #4 on bank 2. Bank 2 always refers to the side of the engine that does not contain cylinder #1. To determine which sensor is knock sensor #4, refer to a vehicle-specific repair source.
The knock sensor is typically threaded directly into the engine block and is a piezoelectric sensor. The location of the sensors in a multi-sensor system may vary between manufacturers, but most are located on the sides of the block, between water jacket freeze plugs. Knock sensors that are on the sides of the engine block are often threaded directly into engine coolant passages. It is important to note that removing these sensors when the engine is warm and the engine cooling system is under pressure can result in severe burns from hot coolant. Therefore, before removing a knock sensor, allow the engine to cool and dispose of the coolant properly.
The knock sensor contains a piezoelectric sensing crystal, which produces a small amount of voltage when shaken or vibrated. Since the knock sensor control circuit is usually a one-wire ground circuit, the PCM recognizes the voltage generated by the vibration as engine noise or vibration. The severity of the vibration experienced by the piezoelectric crystal inside the knock sensor determines the level of voltage produced in the circuit.
If the PCM detects a level of knock sensor voltage that indicates spark detonation, it may retard ignition timing and not store a knock sensor control code. However, if the PCM detects a level of knock sensor voltage that indicates a more severe engine noise, such as a connecting rod contacting the inside of the engine block, it may discontinue fuel delivery and ignition spark to the affected cylinder, and a knock sensor code will be stored.
Severity of the Code & Symptoms
A stored code P033A should be considered severe because it could indicate internal engine failure.
Symptoms of this code may include:
Causes
Potential causes for this code to be set are:
Diagnostic and Repair Procedures
To diagnose a code P033A, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle-specific repair resource. If the engine sounds like it is knocking or excessively noisy, address that issue before attempting a diagnosis for any knock sensor codes.
Check for technical service bulletins (TSBs) that may apply to your year/make/model. If there is a known issue, there may be a bulletin that can help with diagnosis and repair specific to your exact problem, saving you time and money.
Start with a visual inspection of all system-related wiring harnesses and connectors. Look for corroded, burnt, or otherwise damaged wiring and connectors that may create an open or shorted circuit. Knock sensors are often located in the lower part of the engine block, making them susceptible to damage during the replacement of heavy parts like starters and engine mounts. System connectors, wiring, and fragile knock sensors are frequently broken during repairs in the vicinity.
Connect the OBD-II scanner to the vehicle diagnostic connector and retrieve all stored diagnostic codes and freeze frame data. Write down this information for use in the diagnostic process. Clear the codes and test drive the vehicle to see if any are reset.
If the P033A code is reset, start the engine and use the scanner to observe knock sensor data. If the scanner indicates that knock sensor voltage is not within the manufacturer’s specifications, use the DVOM to test live data at the knock sensor connector. If the signal at the connector is within specs, suspect a wiring issue between the sensor and the PCM. If the voltage at the knock sensor connector is not within specifications, suspect a defective knock sensor. If replacing the sensor is the next step, be sure to avoid contact with hot coolant and wait for the engine to cool before removing the old sensor.
