Fault code P033B – knock sensor circuit range/performance (Bank 2, Sensor 4)

Fault code P033B is called “Knock Sensor (KS) Circuit Range/Performance (Bank 2, Sensor 4)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P033B

This diagnostic trouble code (DTC) is a generic code. Error P033B is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P033B – knock sensor circuit range/performance (Bank 2, Sensor 4)

The detonation sensor (KS) is installed in the engine and is used to detect spark detonation. When a spark plug or knock occurs, the sensor outputs a voltage signal which is sent to the PCM. The PCM will then change the ignition advance angle to protect the engine.

Inside the detonation sensor is a piezoelectric crystal. This crystal is used to create an alternating voltage during vibration. That is, it is a kind of transducer that converts changes in physical quantities into an electrical signal.

The detonation sensor (KS), as a rule, has two wires. One supplies 5 volts to the sensor, and the second one transmits parameters from the detonation sensor to the PCM, it is a signal wire.

The sensor signal wire tells the PCM when the detonation occurs, and how strong it is. The PCM then slows the ignition timing to avoid premature detonation. Most PCMs are capable of detecting spark detonation trends in the engine during normal operation.

Error code P033B means the detonation sensor circuit performance range is not correct. That is, the PCM has detected a problem with the detonation sensor or its circuit. Some vehicles may be equipped with more than one detonation sensor. This code refers to sensor 4 on bank 2, the side of the engine that does not have cylinder 1.

Symptoms of vehicle malfunctions

The main signal that an error P033B has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will light up (the code will be written in the memory as a malfunction).
  2. The engine may run, but with reduced performance (power drop).
  3. Jerking, as well as detonation in the engine.
  4. Increased fuel consumption.
  5. There may be no symptoms other than a stored fault code.

The error P033B is not considered very serious. If it occurs, it is unlikely to cause serious problems with the car controllability, but there may be a slight drop in engine power.

Factors that can cause this error code

The error code P033B can mean that one or more of the following problems have occurred:

  • Detonation sensor is defective and requires replacement.
  • Faulty or short circuit in detonation sensor circuit.
  • Incorrect fuel octane rating.
  • Sometimes the cause is a defective PCM module.

How to fix or reset OBD-2 code P033B

Some suggested steps for troubleshooting and fix the error code P033B:

  1. Visually inspect the electrical wiring and connectors to the sensor.
  2. Check continuity of wiring from PCM to detonation sensor wiring connector.
  3. Measure detonation sensor resistance and compare to factory specifications.
  4. Replace the detonation sensor if necessary.

Note that there are two types of detonation sensors, the resonant barrel type and the broadband washer ring type.

Diagnose and repair of problems

Begin diagnostics by visually inspecting all system-related wiring harnesses and connectors. Inspect electrical circuits, sensors, and connectors that are contaminated with engine oil, coolant, or power steering fluid.

Petroleum-based fluids are known to corrode protective wire insulation and short or open circuits. This may cause the error P033B to appear.

Sensor test

To test the old-style detonation sensor, connect a multimeter set to AC voltage between the sensor output wire and ground. Tap the engine near the sensor. You should see the AC voltage value on the digital multimeter. If not, the sensor is faulty and must be replaced.

To test the resonant type sensor, connect the digital multimeter in the same way. But instead of tapping on the engine block. It is necessary to remove the fuel pump relay to prevent the engine from starting.

Crank the engine, put it in gear and keep your foot on the brake. As soon as the car starts to run out of fuel, it will start tapping and stalling. You should then see an AC output voltage. If not, the detonation sensor is faulty and needs to be replaced.

Check the electrical circuits

If the detonation sensor is working properly, but the P033B code is still lit, you need to check the sensor circuit. Using a digital multimeter set to resistance, connect one side of the meter to the wiring harness side of the sensor connector. And the other to the detonation sensor input pin on the PCM. This way we will check the continuity of the circuit between the sensor and the PCM.

Now it is necessary to check the grounding. Old type detonation sensors are grounded through the sensor itself, while new type sensors usually have a separate ground circuit. Connect the red wire of the multimeter to the positive terminal of the battery and the black wire to the ground. You should see a value of about 12 volts, indicating good grounding. If not, you should look for a faulty circuit.

On which vehicles does this problem occur most frequently

Fault code P033B can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chevrolet
  • Ford
  • Toyota
  • Volkswagen

Fault code P033B can sometimes be found with other errors. The most common are the following: P033A, P033C, P033D, P033E.


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