Technical Description of OBD-II Trouble Code
The knock sensor 4 circuit on bank 2 is experiencing low voltage.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles such as Dodge, Ram, Ford, GMC, Chevrolet, VW, Toyota, etc. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
A P033C trouble code indicates that the powertrain control module (PCM) has detected a lower than expected sensor reading from knock sensor #4 on bank 2. Bank 2 refers to the bank of engine cylinders that does not contain the #1 cylinder. 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 may vary between manufacturers, but most are located on the sides of the block between water jacket freeze plugs. Knock sensors on the sides of the engine block are often threaded into engine coolant passages. It is important to allow the engine to cool and dispose of coolant properly before removing a knock sensor to avoid burns from hot coolant.
The knock sensor contains a piezoelectric sensing crystal that produces a small amount of voltage when shaken or vibrated. The PCM recognizes the voltage generated by the vibration as engine noise or vibration since the knock sensor control circuit is normally a one-wire ground circuit. The severity of the vibration determines the level of voltage produced in the circuit.
If the PCM detects knock sensor voltage indicative of spark detonation, it may retard ignition timing without storing a knock sensor control code. If the PCM detects a higher level of knock sensor voltage indicating 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 store a knock sensor code.
Code Severity & Symptoms
A stored code P033C should be considered severe as it could indicate internal engine failure.
Symptoms of this code may include:
Causes
Possible causes for this code to set are:
Diagnostic and Repair Procedures
To diagnose a code P033C, 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 to assist with diagnosis and repair specific to your problem, saving you time and money.
Begin with a visual inspection of all system related wiring harnesses and connectors. Look for corroded, burnt, or 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 and can be susceptible to damage during repairs involving 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 P033C 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 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 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.
