needanotherholiday.com is supported by its audience. As an Amazon Associate, we earn affiliate commissions from qualifying purchases. Learn more:

P0138 Code Toyota (What & Why)

If you’re a Toyota owner, you must have seen the “P0138” code pop up on your vehicle’s display. Therefore, this trouble P0138 Code Toyota indicates that there is an issue with the bank 1 oxygen sensor.

Since the bank 1 oxygen sensor is located before the catalytic converter on the exhaust system.

When this sensor goes bad, it can cause a decrease in fuel efficiency and an increase in emissions.

In some cases, it can also cause the engine to run lean, which can lead to engine damage.

If you see this code appear on your vehicle’s display, it’s important to take it to a qualified mechanic as soon as possible so they can diagnose and repair the problem.

P0138 Code Toyota (A to Z)

The P0138 code is a generic OBD-II trouble code that indicates an issue with the bank 1, sensor 2 oxygen sensor.

This particular code is defined as “O2 Sensor Circuit High Voltage” and usually means that there is a problem with the wiring or connectors to the sensor, or possibly the sensor itself.

In order to troubleshoot this code, it’s important to first understand how the oxygen sensors work.

The oxygen sensors are located in the exhaust stream and measure the amount of oxygen in the exhaust gas.

However, the engine control module (ECM) uses this information to adjust the air/fuel mixture so that it can run as efficiently as possible.

If there is an issue with one of the oxygen sensors, it will throw off the air/fuel mixture and cause your vehicle to run less efficiently.

In fact, it can also cause your vehicle to run too rich or too lean, which can lead to other problems such as increased emissions or decreased fuel economy.

Further, to diagnose this code, you will need a scanner that can read live data from the ECM.

Once you have access to this data, you should check for any codes related to Oxygen Sensor Circuit High Voltage: P0133, P0134, P0135 or P0136 .

If any of these codes are present along with P0138, they will need to be addressed first before troubleshooting P0138.

If there are no other codes present, then you will want to start by checking all of the wiring and connectors going to your bank 1 oxygen sensor 2.

  • Make sure there are no loose connections or damaged wires. If everything looks good here, then you will want move on testing voltage at different parts of circuit using a voltmeter.
  • Start by testing voltage at connector E13 pin 4 (oxygen sensor power supply). You should see around 0.6-0.7 volts here when engine is running idle. If not, then check fuse F3 in underhood fuse box for open circuit.
  • Next, test voltage at same connector E13 but on pin 3 this time (ground). With key on engine off, you should see 12 volts here but if not, then check continuity between E13 pin 3 and ground point G103.
  • Now test voltage again at connector E13 but on pin 2 this time(signal wire).

Causes of P0138 Code

If you own a car, chances are you’ve seen a “check engine” light come on at some point. This light is part of your car’s On-Board Diagnostics (OBD) system, and it comes on when the OBD system detects an issue with your vehicle.

One of the most common codes that will creat the check engine light is P0138.

P0138 code indicates that the OBD system has detected a problem with the oxygen sensor signal in the exhaust stream.

The oxygen sensor couuld be the reason for monitoring the amount of oxygen in the exhaust gas and sending a signal to the engine control unit (ECU).

If there is too much or too little oxygen in the exhaust, it can cause problems with how the engine runs.

There are a few things that can cause P0138 code to be initiated:

1. Faulty Oxygen Sensor:

The most common cause of this code is a faulty oxygen sensor. Over time, these sensors can become worn out or damaged and stop working properly.

If this is the case, you’ll need to replace your oxygen sensor to fix the problem.

2. Exhaust Leak:

Another possible cause of P0138 code is an exhaust leak before or after the oxygen sensor itself. This can throw off readings from the sensor and trigger a false P0138 code.

To diagnose this, you’ll need to use a smoke machine to check for leaks in your exhaust system.

3. Loose or Damaged Wiring:

In some cases, loose or damaged wiring may be causing interference with signals from the oxygen sensor and triggering a P0138 code.

This is usually an easy fix and can be fixed by tightening or replacing wiring as needed.

4. Fuel Pressure Issue:

Another possible cause of P0138 code is a fuel pressure issue. If your fuel pressure drops below specifications it can affect how well your engine run sand may trigger a P0138 code. 

You’ll need to test your fuel pressure to rule this out as cause.

5. ECU Issue:

An issue with your ECU may be causing P0138 code to be triggered.

If all other potential causes have been ruled out, then this may be something that needs to be addressed by a professional mechanic or dealership service department.

How to Fix P0138 Code in 3-Steps

It’s not so tough to fix this error by your own. With some basic mechanical knowledge (as a car owner or driver) you can fix this trouble quickly.

If you have a P0138 code, it can cause your engine to run lean or rich. Whenever, your check engine light is on and you’re getting a P0138 code, it’s time to take action.

When there is an issue with this sensor, it can cause problems with your engine’s performance.

As you know, the oxygen sensor is main reason for monitoring the amount of oxygen in the exhaust gases, and if it detects that there’s too little oxygen, it will trigger the check engine light.

There are 3-quick steps you can take to fix this problem:

1) Check the Oxygen Sensor

The first thing you should do is make sure that the oxygen sensor itself is working properly. You can do this by testing it with a multimeter.

If the sensor is damaged or defective, then you’ll need to replace it.

2) Check for Exhaust Leaks

Another possible cause of the P0138 code is an exhaust leak. To check for leaks, start by inspecting all of the rubber hoses and gaskets in your exhaust system.

If you see any cracks or damage, then you’ll need to replace those parts.

Once you’ve replaced all of the damaged parts, make sure to retest your vehicle to see if the code has gone away.

3) Check the Catalytic Converter

The catalytic converter helps to convert harmful emissions into harmless gases before they’re released into the atmosphere.

If your catalytic converter isn’t working properly, it could be causing the Po138 code.

To test it, use a multimeter to measure its output voltage while your vehicle is running. If the reading is lower than normal, then you’ll need to replace your catalytic converter

How to Avoid P0138 Code Toyota

Proper maintaining can be the best way to avoid the troubles. However, there are a few things you can do to avoid getting the P0138 code on your Toyota.

Always using the correct octane fuel for your engine keeps you far far away form this hassle. If you use lower octane fuel than what is recommended, it can cause knocking and pinging which can damage the oxygen sensor.

Keep an eye on your air filter and replace it when necessary, since a dirty air filter will restrict airflow to the engine and can cause the oxygen sensor to overheat.

You also have to be sure that your exhaust system isn’t leaking. Thus, e

xhaust leaks can lead to false readings from the oxygen sensor. If you follow these steps, you should be able to avoid getting the P0138 code on your Toyota.

  • Check your oil level and quality regularly, if your oil is low or dirty, it can cause your engine to run less efficiently, making the P0138 code.
  • Keep an eye on your oxygen sensor, a faulty oxygen sensor can cause the P0138 code to be caused.
  • Make sure your exhaust system is functioning properly, a clogged or damaged exhaust system can cause the P0138 code to be triggered.
  • Have your vehicle serviced regularly by a qualified technician, thus this will help ensure that all of your vehicle’s systems are functioning properly and can help prevent codes like the P0138 from being occured in the future.

P0138 Bank 1 Sensor 2 Location

This P0138 Code Toyota is a common trouble code associated with the oxygen sensor in your vehicle.

Basicly, the oxygen sensor is located in the exhaust system and monitors the level of oxygen in the exhaust gases.

If the oxygen sensor detects that there is too much oxygen in the exhaust, it will trigger the P0138 code.

This can be caused by a number of things, including a faulty oxygen sensor, an air leak in the intake system, or a problem with the fuel injectors.

In some cases, this code may also be triggered by a problem with one of the cylinders in your engine.

P0138 Upstream Or Downstream

If your car’s check engine light is on, and you’ve determined that the code P0138 is the cause, it means that the oxygen sensor in your car’s exhaust system is not working properly.

The oxygen sensor is responsible for monitoring the amount of oxygen in the exhaust gas as it exits the engine.

If there’s too much or too little oxygen, it indicates that the air-to-fuel ratio in the engine is off, and adjusting it can improve fuel economy and performance.

There are two types of oxygen sensors: upstream and downstream.

Upstream sensors are located before the catalytic converter, while downstream sensors are located after. In most cases, P0138 refers to a problem with an upstream sensor.

The sensor produces a small voltage that increases as the oxygen level decreases. And this signal is then sent to the computer, which adjusts the air/fuel mixture accordingly.

If your check engine light is on and you’ve diagnosed a P0138 code, it means that the oxygen sensor downstream from the catalytic converter isn’t working correctly.

This can be caused by a number of things, including:

  • A faulty Oxygen Sensor
  • A problem with the wiring or connectors
  • Exhaust leaks upstream of the sensor

What Can Cause an O2 Sensor to Throw a Code?

If your car’s oxygen sensor is faulty, it will usually throw a diagnostic trouble code. There are 4-major reasons that can cause an oxygen sensor to fail, including:

  1. Oil contamination: If oil gets on the oxygen sensor, it can cause the sensor to produce inaccurate readings.
  2. Fuel contamination: If fuel gets into the oxygen sensor, it can also cause inaccurate readings.
  3. Exhaust leaks: If there are any leaks in the exhaust system, it can allow unburned fuel to enter the oxygen sensor, which will again cause inaccurate readings.
  4. Faulty spark plugs: If the spark plugs are not firing correctly, it can affect the air/fuel mixture and cause the oxygen sensor to produce inaccurate readings.

O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)

An O2 sensor circuit high voltage code (P0172) on Bank 1 Sensor 1 indicates that the oxygen sensor’s signal is reaching the PCM outside of the normal range.

This can happen for a number of reasons, but most often it’s caused by a problem in the fuel delivery system.

If you’re getting this code, here are 2-things to check:

Check all your fuel injectors for proper operation: A clogged or leaking injector will cause too much fuel to be delivered to the engine, resulting in a rich air/fuel mixture. This can trigger a P0172 code.

Inspect your air filter: If it’s dirty or restricted, it could be starving the engine for air, causing a lean condition and setting off the P0172 code.

Make sure there are no vacuum leaks in the intake system. Even a small leak can cause enough of a change in airflow to set off a P0172 code.

Causes an Oxygen Sensor to Have High Voltage

An oxygen sensor is a key component in the emissions control system of your vehicle. Thereofore, the oxygen sensor monitors the amount of unburned oxygen in the exhaust as it exits the engine.

The computer uses this information to adjust the air/fuel mixture to keep it at the optimum level for emissions and performance.

If an oxygen sensor is producing high voltage, it’s an indication that there is too much unburned oxygen in the exhaust.

This can be caused by a number of things, including:

  • A rich air/fuel mixture (too much fuel, not enough air)
  • An incorrect spark plug gap
  • Leaking injectors

Causes of Oxygen Sensor Low Voltage

An oxygen sensor produces a corresponding electrical signal that is proportional to the oxygen concentration. The most common type of oxygen sensor is the zirconia oxygen sensor.

The main function of an oxygen sensor is to help your car’s engine run as efficiently as possible. That’s because it provides information to the engine control unit (ECU) about how much oxygen is in the exhaust stream.

Based on this data, the ECU can make adjustments to ensure that the air-fuel mixture going into the engine is optimal for combustion.

If an oxygen sensor detects that there’s not enough oxygen in the exhaust, it will send a low voltage signal to indicate that more fuel needs to be injected into the cylinders.

On the other hand, if too much oxygen is detected, a high voltage signal will be sent and less fuel will be injected. Maintaining the correct air-fuel ratio is crucial for proper engine operation and performance.

There are a number of things that can cause anoxygen sensor low voltage condition:

1) A rich air/fuel mixture: This can happen if there’s a problem with fuel injectors or carburetor jets that result in too much fuel being delivered to the cylinders.

An overabundance of fuel will cause unburned hydrocarbons to end up in the exhaust stream, resulting in a decreased output fromthe oxygen sensors.

2) Lean air/fuel mixture: If there isn’t enough fuel reachingthe cylinders, then obviously there won’t be enough for complete combustion.

This can leadto an excessively high outputfromtheoxygensensorsas they tryto makeupfor lackofoxygenin exhastedgas by sendinga higherthan normalvoltage signal backto ECU.

3) Exhaust leaks: If your car has any sort of leak intheexhaust systembeforeorexitingtheoxygensensor,it couldbe throwingoff its readingsand causing ittosendincorrect signalsbackto theeCU.

4) Faulty oxygensensor: Over timeandwith extended use, o2sensorwillwear outand become less accurateintheir readings.

If yoususpectyour o2sensor maybegoing badyou shouldhaveittestedorreplacedbyaprofessionalmechanic.

Most Common FAQs about Engine Traouble Code P0138

What Causes an Oxygen Sensor to Have High Voltage?

An oxygen sensor is a key part of a car’s emissions control system, and it monitors the oxygen levels in a car’s exhaust.

Moreover, the sensor then sends this information to the car’s computer, which uses it to adjust the air/fuel mixture so that the engine runs as efficiently as possible.

Over time, though, oxygen sensors can become less accurate, and when this happens, they may send incorrect signals to the computer.

Though this can cause the engine to run too rich or too lean, and it can also cause high voltage readings.

There are a few things that can cause an oxygen sensor to have high voltage:

  • A faulty or damaged oxygen sensor
  • A build-up of deposits on the sensor (from oil, fuel additives, etc.)
  • Exhaust leaks upstream of the sensor

If you’re getting high voltage readings from your oxygen sensor, it’s important to have it checked out by a mechanic so that they can diagnose and fix the problem.

Can You Drive With a P0138?

Yes, you can drive with a P0138.

However, it is important to note that this code indicates that there is an issue with the oxygen sensor signal circuit in your vehicle.

Potentially it will lead to decreased fuel economy and increased emissions, so it is something that should be addressed as soon as possible.

Can an Exhaust Leak Cause a P0138 Code?

An exhaust leak can most definitely cause a P0138 code. In fact, it is one of the most common causes of this particular code.

The P0138 code indicates that there is an issue with the oxygen sensor located on the bank 1 sensor 2 position.

Clearly, this means that there is a problem with the way that the oxygen sensor is measuring the amount of oxygen in the exhaust stream.

When there is an exhaust leak, it can allow outside air to enter into the system and throw off the readings of the oxygen sensor.

So, this will cause your vehicle to run leaner than it should be and can lead to all sorts of other issues.

Therefore, if you have a P0138 code, it’s definitely worth checking for an exhaust leak before anything else!

Can a Bad Catalytic Converter Cause a P0138 Code?

A catalytic converter is an important part of a car’s emission control system, and it can cause problems if it goes bad.

A bad catalytic converter can cause a P0138 code, which means that the oxygen sensor in the exhaust system is not working properly.

The oxygen sensor is used to monitor the amount of oxygen in the exhaust gas, and it sends a signal to the engine computer when it detects a problem.

If the oxygen sensor is not working properly, the engine will run too rich or too lean, and this can damage the catalytic converter.

What Causes Oxygen Sensor Low Voltage?

The most common causes of oxygen sensor low voltage is a faulty or damaged oxygen sensor.

Since the oxygen sensor is responsible for measuring the amount of oxygen in the exhaust gas and sending a signal to the engine control unit (ECU).

If the oxygen sensor is damaged, it can send a false signal to the ECU, causing the engine to run leaner than it should.

Thus, this can lead to a decrease in fuel economy and an increase in emissions.

What Causes High Voltage in Downstream O2 Sensor?

One of the most common causes of a high voltage reading from a downstream oxygen sensor is a faulty or damaged sensor.

If the sensor is not functioning properly, it will send inaccurate readings to the engine control unit (ECU) and this can cause the ECU to make incorrect adjustments to the air/fuel mixture, which can lead to decreased fuel economy and increased emissions.

Other potential causes of high voltage readings from downstream oxygen sensors include rich air/fuel mixtures (caused by leaking injectors or excessively rich carburetor settings), lean air/fuel mixtures (caused by vacuum leaks or restricted airflow), and excessive exhaust gas temperatures (caused by improperly functioning catalytic converters or exhaust gas recirculation systems).

Final Words

If your Toyota has the P0138 code, it means that the air/fuel mixture in the engine is too lean.

This can be caused by a number of things, including a faulty oxygen sensor, a leak in the intake manifold, or a problem with the fuel injectors.

If you have this code, it’s important to get it fixed as soon as possible because it can lead to engine damage.

Leave a Comment