Fault code P2238 – O2 sensor positive circuit control circuit low (Bank 1, Sensor 1)

Fault code P2238 is called “O2 Sensor Positive Circuit Control Circuit Low (Bank 1, Sensor 1)” 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 P2238

Stored code P2238 means that the Powertrain Control Module (PCM) has detected a low plus circuit signal in Oxygen Sensor 1 for Cylinder Bank 1. To monitor the oxygen content in the exhaust gases. As well as the efficiency of the catalytic converter, the PCM uses input from the heated oxygen sensors (HO2S).

Fault code P2238 – O2 sensor positive circuit control circuit low (Bank 1, Sensor 1)

The oxygen sensors are designed with a zirconium dioxide sensing element located in the center of the vented steel housing. Small platinum electrodes are soldered between the sensing element and the wires in the oxygen sensor harness connector. The O₂ sensor harness connector connects to the Controller Area Network (CAN), which connects the oxygen sensor harness to the PCM connector.

Each HO2S sensor, is positioned so that the sensing element is closer to the center of the pipe. Exhaust gases enter the oxygen sensor through special holes in the steel housing and pass around the sensing element. The heated air causes the oxygen ions to produce energy, which is recognized as voltage by the PCM.

As the pulsating oxygen ions move between the platinum layers, changes in the HO2S output voltage occur. The PCM senses these changes in the oxygen sensor output voltage as changes in the oxygen concentration in the exhaust.

If the PCM detects a voltage level that is not within acceptable parameters. Error code P2238 will be stored, and the Malfunction Indicator Light (MIL) may illuminate.

Most vehicles will require several ignition cycles (if failing) for the check lamp to illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P2238 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 light on the control panel will illuminate (the code will be written to the ECM memory as a fault).
  2. Additionally, ignition misfire and lean/rich exhaust codes may be present.
  3. Loss of engine power.
  4. The engine does not accelerate well, or there may be vibration during acceleration.
  5. Increased fuel consumption.

Fault code P2238 is considered serious. Since a short circuit of the O₂ sensor may cause very poor engine performance and various steering problems.

Factors that can cause this error code

The error code P2238 can mean that one or more of the following problems have occurred:

  • Oxygen sensor O₂ is defective.
  • Problem with connection wires and connector as melted or broken.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P2238

Some suggested steps for troubleshooting and fix the error code P2238:

  1. First, connect an OBD-II scanner to the vehicle’s onboard computer and read all stored data and error codes.
  2. Then clear the error codes from the PCM memory and test-drive the vehicle to see if error P2238 appears again.
  3. If the error code appears again, check the wires and connectors.
  4. Test the sensor and replace if necessary.

Diagnose and repair of problems

Connect the scan tool to the vehicle’s diagnostic port and retrieve all stored codes. Then clear them and test-drive the vehicle. If the code does not appear, then the error was temporary. If it appears, continue testing.

Perform a visual inspection of the wiring and connectors associated with the oxygen sensor (HO2S). Replace damaged wiring or connectors if any damage is found. After that, reset the errors again, test drive and read them again.

If code P2238 is found again, start the engine. Allow it to warm up to normal operating temperature at idle. Connect the scan tool to the diagnostic port and observe the oxygen sensor inputs.

If the oxygen sensor O₂ is functioning normally, the voltage in front of the catalytic converter will change continuously from 1 to 900 millivolts. The sensors after the catalyst will also cycle between 1 and 900 millivolts. An HO2S sensor that is not working properly should be considered faulty if the engine is in good working order.

If the HO2S sensor is displaying battery voltage or no voltage in the scan tool data stream. Use a multimeter to get live data from the HO2S sensor connector. If the output is still the same, then the HO2S sensor has shorted out and will need to be replaced.

It may happen that after running all the tests, code P2238 is still displayed, it most likely indicates a faulty oxygen sensor O₂. But a failed PCM module also cannot be ruled out until the sensor is replaced.

On which vehicles does this problem occur most frequently

Fault code P2238 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Acura
  • Audi
  • BMW
  • Honda
  • Hyundai (Matrix, Starex)
  • Kia (Sorento, Soul)
  • Lexus (RX330, RX350)
  • Mazda
  • Peugeot
  • Skoda
  • Toyota (4Runner, Camry, Corolla, Crown, Echo, Prado, Prius, RAV4, Sienna, Tundra)
  • Volkswagen (Passat)

Fault code P2238 can sometimes be found with other errors. The most common are the following: P2195, P2237, P2239, P2240, P2241, P2242.


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