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P0134 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


A P0134 trouble code stands for O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1).


The oxygen sensor reads the amount of oxygen and fuel that comes through the exhaust. This is a safety precaution to make sure the oxygen to fuel ratio is correct. The oxygen sensor sends that information to the power control module (PCM) of the vehicle

If at any time there is an insufficient amount of oxygen in the exhaust, the PCM will decrease the amount of fuel that is being used by the motor. The reason that this is important is if there is an insufficient amount of oxygen in the exhaust, the car will use a greater amount of fuel and emit an increased amount of carbon monoxide into the air.

If there is an inadequate amount of fuel going into the exhaust, the PCM will increase the amount of fuel being used by the motor. This is critical because if there is an insufficient amount of fuel in the exhaust, the car will emit hydrocarbons and nitrogen oxides into the air.


There are a few key causes that are responsible or related to a P0134 trouble code:

  • A faulty heater circuit.
  • A wire that is disconnected or broken from the oxygen sensor.
  • Corrosion in the connectors.
  • A leak in the engine vacuum.
  • A faulty power control module (PCM).

Any one or more of these reasons could cause a P0134 trouble code to populate on your OBD-II scanner.

Is it possible for a bad O2 sensor to cause a lean code?

An engine vacuum leak, low fuel pressure, or dirty fuel injectors might be the real problem instead of a bad O2 sensor. A contaminated O2 sensor is often the cause of a sensor failure, especially a premature one.


If you are driving the vehicle, there are some symptoms to look out for when you are trying to spot an OBD-II trouble code:

  • The Check Engine Light on the dashboard may come on.
  • The engine may stall.
  • The car may be running rough or idling poorly.
  • You may smell something like rotten eggs and/or see black smoke that is coming from the exhaust.

Keep in mind that there are times when a driver will not notice any of these symptoms, other than the Check Engine Light is on. This is a rare occurrence, but it is possible when experiencing a P0134 trouble code.


Make sure that you stick to the following steps for diagnosing this problem with a vehicle: A technician will use an OBD-II scanner to diagnose the P0134 code.

  • The freeze frame data should be captured in order to determine when the code was first set. At this point, the code should be reset and the vehicle test-driven.
  • While test driving the vehicle, it will need to reach normal operating temperature in order for you to see if the code comes back.
  • If the fault code does come back, the wiring that goes to the oxygen sensor and grounds should be inspected.
  • While inspecting, your technician should look for breaks and corrosion. Live data should be observed in an effort to determine whether the millivolt valves are going low to high.
  • The oxygen sensor should also be inspected in order to determine whether it has power going to it and that it is receiving the proper signal voltage from the Power Control Module (PCM).

Common mistakes

Keep in mind that there are some common mistakes that even experienced mechanics and technicians can experience when diagnosing a P0134 trouble code:

A mistake that is commonly made when diagnosing the code p0134 is assuming that the oxygen sensor is the first thing that needs to be replaced without first considering other possibilities for the source of the problem.

Sometimes the oxygen sensor itself is not the problem. This can mean there are other things that could prevent the oxygen sensor from working, such as the wiring to the oxygen sensor. The wiring should be inspected and ruled out as the cause before you replace the oxygen sensor.

How serious is this?

It is unlikely the code p0134 will prevent the driver or owner from operating the vehicle.  It should start and run, but the driver may experience a lack of power.

Driving with a P0134 trouble code could cause damage to the catalytic converter but it would take an extended period of time to do so. What is most impactful with this trouble code is that it is common for there to be a decrease in fuel economy. That means the car will burn fuel at a higher rate of speed. For this reason, it is important to have a technician complete diagnosis of the code, as well as make the necessary repair as soon as possible.

What repairs can fix the code?

There are a few common repairs that can fix this trouble code:

  • The technician should use a scanner to validate the fault code. After the fault code has been validated, it should be reset and a test drive should be performed. If the Check Engine Light returns with the same fault code, an inspection should follow.
  • The wires and connectors should be inspected for any damage. If the wires and connectors are damaged, they should be repaired or replaced. Reset fault code and test drive.
  • If the Check Engine Light comes on again and the technician gets the same code, the oxygen sensor will need to be replaced.
  •  If the P0134 trouble code comes back after replacing the oxygen sensor, the exhaust pipe and heater fuse should be inspected to rule out possible damage of the two.

Related codes

None listed.


Though a P0134 may not be detrimental to the life or drivability of the vehicle, this is an issue that the driver should get inspected, tested, and diagnosed immediately.

P0134 Code – What Does It Mean & How To Fix It