P0134 - Oxygen (A/F) Sensor No Activity Detected (Bank 1 Sensor 1)

The air fuel (A/F) ratio sensor or as it's often called front oxygen sensor (Bank 1 Sensor 1), measures the amount of oxygen in the exhaust. Based on its signal, the engine computer adjusts the fuel/air ratio to keep it at the optimum level. Read more about the air fuel ratio sensor. The code P0134 means that the signal from the air fuel ratio sensor does not change for a certain time when the necessary conditions (engine temperature, rpm, etc.) are met. Often this code is caused by a faulty air/fuel ratio sensor, but there are other possibilities:

What can cause the code P0134:

- a faulty air/fuel ratio sensor (front oxygen sensor)
- open or short in the oxygen sensor wiring or connector
- open or short at the oxygen sensor heater circuit
- bad sensor ground
- exhaust leaks
- a faulty engine computer (ECM)
- lean air/fuel mixture


A service bulletin for 2006-2008 Honda Civic Si describes a problem where the grease would drip onto the air/fuel (A/F) ratio sensor connector causing the code P0134 or some other codes. Honda recommends replacing the A/F sensor and installing a sub-harness kit as a solution.
In some Hyundai V6 engines, a faulty oxygen sensor could cause the code P0134 along with misfiring codes (P030x) and rich condition; replacing the oxygen sensor should solve the problem.
A TSB for 2000-2001 Nissan Maxima mentions possible intermittent connection at the ECM causing the code P0134 or others.
A bad front air/fuel ratio sensor causing the code P0134 is a common occurrence in some Honda vehicles. A new air/fuel ratio sensor usually fixes the problem.
In some Volkswagen cars, a bad mass air flow sensor could cause a lean condition that could in turn cause the code P0134 along with some other fault codes.

What needs to be checked:

If there are other trouble codes stored along with the P0134, they might need to be looked at first. In a V6 or V8 engine, if there is a code P0154 Oxygen (A/F) Sensor No Activity Detected (Bank 2 Sensor 1) stored along with the P0134, the problem is more likely not with the oxygen sensors, as both sensors would not go at the same time.
First, the air/fuel ratio sensor connector, as well as the sensor power and ground must be checked. Next, the wiring between the PCM and the air fuel sensor must be tested. If no other problems found, the sensor must be replaced.

How the air fuel ratio sensor is checked with a scan tool:

The air fuel ratio sensor readings are checked after the engine is fully warmed up. The signal voltage or current should stay within specified value. See Honda air fuel ratio sensor current displayed on a scan tool. When the engine is revved, the signal should change. When repairing the code p0134, your mechanic may recommend replacing the air fuel ratio sensor first, even if it appears to be working at the moment. This make sense to eliminate the possibility of the sensor having intermittent problems. Plus, in many cars, the air fuel ratio sensor deteriorates over time anyway.

Air fuel ratio sensor replacement

Replacing air fuel ratio sensor
Replacing the air fuel ratio sensor

When replacing the front oxygen or air fuel ratio sensor, it's always recommended to use an OEM part. There are cases where an incompatible aftermarket air fuel ratio sensor can cause the code P0134. If the vehicle is California certified, it might need a special air fuel ratio sensor. Your dealer can verify the correct part number by your vehicle's VIN number. Replacing the air fuel ratio sensor ratio sensor may cost from $50 to $150 labor plus $65-$320 part. To replace the sensor as a DIY project you might need a special oxygen sensor socket, as in the photo.

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