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P0138 Toyota Code - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2

Quick Answer

In order to obtain a high purification rate of the Carbon Monoxide (CO), Hydrocarbon (HC), and Nitrogen Oxide (NOx) components in the exhaust gas, a Three-Way Catalytic Converter (TWC) is used. Common causes include Faulty Oxygen Sensor Bank 1 Sensor 2, Oxygen Sensor Bank 1 Sensor 2 harness is open or shorted, Oxygen Sensor Bank 1 Sensor 2 circuit poor electrical connection. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means
P0138 Toyota indicates Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2.
Common causes
Common causes include Faulty Oxygen Sensor Bank 1 Sensor 2, Oxygen Sensor Bank 1 Sensor 2 harness is open or shorted, Oxygen Sensor Bank 1 Sensor 2 circuit poor electrical connection.
Severity
Moderate - service should be scheduled soon.
Can I drive?
The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
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Code Popularity 151,992
How popular is this code, among other codes? High
What is this?
Table of contents Created and updated by William Orellana on Aug 24, 2022
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Code P0138 Toyota Description

In order to obtain a high purification rate of the Carbon Monoxide (CO), Hydrocarbon (HC), and Nitrogen Oxide (NOx) components in the exhaust gas, a Three-Way Catalytic Converter (TWC) is used. For the most efficient use of the TWC, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel level. For the purpose of helping the Engine Control Module (ECM) to deliver accurate air-fuel ratio control, a heated oxygen sensor is used.
The heated oxygen sensor is located behind the TWC and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is high. The heated oxygen sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration in the exhaust gas is low. The heated oxygen sensor informs the ECM that the post-TWC air-fuel ratio is rich (high voltage, i.e. more than 0.45 V). The heated oxygen sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the heated oxygen sensor to determine whether the air-fuel ratio after the TWC is rich or lean and adjusts the fuel injection duration accordingly. Thus, if the heated oxygen sensor is working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel ratio control.
The ECM continuously monitors the heated oxygen sensor output voltage while the engine is running. The Diagnostic Trouble Code (DTC) P0138 is stored if the heated oxygen sensor voltage output is 1.2 V or higher for 10 seconds or more.
OBDII Code P0138 Toyota - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com
P0138 Toyota Code - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2
What does this mean?

What are the Possible Causes of the DTC P0138 Toyota?

  • Faulty Oxygen Sensor Bank 1 Sensor 2
  • Oxygen Sensor Bank 1 Sensor 2 harness is open or shorted
  • Oxygen Sensor Bank 1 Sensor 2 circuit poor electrical connection
  • Gas leak from exhaust system

How to Fix the DTC P0138 Toyota?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

Replacing the Oxygen Sensor Bank 1 Sensor 2 (Rear Oxygen Sensor Bank 1 or Downstream Oxygen Sensor Bank 1) usually takes care of the problem.

There is a Factory Service Bulletin for the following Toyota models:
2005-2007 Toyota Avalon
2007-2008 Toyota Camry
2005-2007 Toyota Avalon, 2007-2008 Toyota Camry Factory Service Bulletin OBDII Code P0138





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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0138 Toyota code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Information for Specific Toyota Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0138 Toyota Code

No Frequently Asked Questions about P0138 Toyota Code found.

Discuss the causes and fixes for P0138 Toyota OBDII Code

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  • I have a 2006 Toyota Tundra 4.7, I just changed both B1s2, b2s2 sensors and both codes P0138/P0158 returned after a couple of days. What should I be looking for? I am going to replace the bosche senors with denso ones, I hope that helps. Could anyone tell me what else I should look for if the codes return after the swap..

    Reply to Comment

    • Me paso lo mismo, solo que nada más era el código PO138, después de probar tres sensores descubrí que tienes que poner exactamente el sensor que maneje la misma resistencia tanto para el calentador como para la resistencia de la señal, de otro modo volverá a aparecer el código, no sé porque, pero cuando cambies el que fallo revisa que el conector sea del mismo color, color de cables, numero de agujeros en los costados y si trae agujero en la punta plana, tuve que hacer eso después de probar tres sensores y por fin se borró el código. Aunque lo borres con el escáner vuelve a aparecen en uno o dos días, hasta que pongas el mismo modelo de sensor.

      Reply to Comment

  • You should also check exhaust leaks and damage sensors wire

    Reply to Comment

  • One more question, when you install the sensors B1S2 and B2S2 do they go to a specific side or can they just be installed randomly?

    Reply to Comment

  • The truck is shutting off after braking.

    Reply to Comment

  • So to update the status, I changed the sensors B1S2/B2S2 from bosche to Denso. And they worked! Thanks for the support, I did however, check all the wires and connections.

    Reply to Comment

  • Congrats! and thank you for letting us know.

    Reply to Comment

  • I am back. So the codes returned today, I used my scanner to see the live data and B1S2 read .950 and B2S2 read .900 and B1S1 read 3,500 and B2S1 read 3,450. In addition when the truck arrived it smelled very bad like exhaust and it was coming from under the driver side, I also, heard a crackling sound the other day when it was cold coming from the manifold and I read that these trucks have that sound when the manifold has a hairline crack in it. Could you give me any support or knowledge on these? Any support is much appreciated.

    Reply to Comment

  • Your next step is to check the wires from the sensor to Engine Control Module (ECM). The P0138 code is for "Oxygen Sensor Circuit High Voltage", circuit high voltage means that there is either a short circuit on the wire harness, you have a bad O2 sensor or bad ECM. Make sure the connector is fully connected and there is no corrosion on the connector.

    Reply to Comment

  • I will check it out and keep you posted. Thank you!

    Reply to Comment

  • How should I read the oms or V on the harness? I am not getting reading with the key on the on position. Can't find a diagram showing which holes to check for v or Ohms.

    Please reply at your earliest convenience.

    Reply to Comment

  • Both B1S1/B2S1 are good with the 12v battery, 3v and ground. The B1S2 and B2S2 both have 12V but no 3v reading and ground looks good. What could be the issue with this? Or what should I be looking for now?

    Reply to Comment

  • If the connector fits, the both sensor should be the same.

    The P0101 code is for the Mass Air Flow (MAF) Sensor, the sensor could affect the O2 sensor reading, but it should trigger other codes, and not the P0138.

    You should try cleaning the MAF first, it's possible that the MAF maybe messing up with the O2 sensors readings.

    The best way to read the sensors is with an scanner, with the scanner you can read if the sensor is actually working and the voltage that is producing. The 12 volts you are reading is for the sensor heater.

    Reply to Comment

  • Ok. Thank you. I cleaned the MAF sensor and cleared the codes. After running for about 20 minutes at 2,500 RPM. I scanned it and retrieved this code for the battery C1241 and a pO305. It has other codes but those are for the airbag knee and rear wheel sensor which have no relation to the problem I think. For the po305 I looked at cylinder #5 and found it was not tighten correctly and after tightening that code cleared and I was left with the C1241. Which I think the serpent belt tensioner pulley is not good anymore. So we will buy that and replace it to see of that code clears. The battery is still good and I cleaned the post and connectors. I will keep you posted on this and thank you for all the help Sir!

    Reply to Comment

  • hi i have a 2006 toyota sienna 3.5 engine where is where bank1 sensor 2 it located

    Reply to Comment

  • Here is the only image I got; It's the number 1 on the image. I hope it helps

    Image

    Click here to enlarge image

    Reply to Comment
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