Fault code P2338 – cylinder 3 above knock threshold

Fault code P2338 is called “Cylinder 3 Above Knock Threshold” 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 P2338

This Diagnostic Trouble Code (DTC) is a generic code. Error P2338 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 P2338 – cylinder 3 above knock threshold

If your vehicle has stored this error code accompanied by a Malfunction Indicator Light (MIL). This means that the Powertrain Control Module (PCM) has detected a signal from the No. 3 cylinder detonation sensor that is outside the allowable threshold value.

The knock sensor (KS) is installed in the engine and is used to detect spark detonation. When a spark knock 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 knock 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 knock 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.

If the PCM detects an unexpected degree of voltage in the cylinder No. 3 detonation sensor circuit, code P2338 will be stored and the MIL indicator will illuminate. It may take several failure cycles for the MIL indicator to be displayed.

Symptoms of vehicle malfunctions

The main signal that an error P2338 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.

Error P2338 can be either minor or very serious, depending on the symptoms. If it occurs, it is unlikely to cause serious driving problems, but the cause should be diagnosed as soon as possible.

Factors that can cause this error code

The error code P2338 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.
  • Detonation sensor connectors are broken or disconnected.
  • Serious mechanical engine problem caused by component failure.
  • Incorrect fuel octane rating.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P2338

Some suggested steps for troubleshooting and fix the error code P2338:

  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 can cause the error P2338 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 not getting enough fuel, it will start tapping and stalling. After that you should 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 P2338 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 we need 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 P2338 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Citroen (C4)
  • Ford (Mondeo)
  • Mercedes-Benz (Sprinter)
  • Nissan
  • Peugeot (3008)

Fault code P2338 can sometimes be found with other errors. The most common are the following: P0251, P1102, P1211, P2336, P2337, P2339, C1123, C1312.

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