P0134: O2 Sensor Circuit No Activity Detected (Bank1 Sensor1)

What is P0134?

Fault code P0134 is a diagnostic trouble code (DTC) defined as “Oxygen Sensor Circuit No Activity Detected (Bank 1 Sensor 1).”

Note: Bank 1 in this trouble code refers to the side of the engine with the number one cylinder.

This engine code means that the powertrain control module (PCM) of your vehicle has detected inactivity from the upstream oxygen sensor (O2 sensor.)

The emission control system of your vehicle consists of two or four oxygen sensors. The upstream sensor is located before the catalytic converter (right before the heat shield), while the downstream oxygen sensor (rear sensor or rear O2 sensor) is located after the converter.

The upstream oxygen sensor is a heated oxygen sensor that keeps track of the amount of oxygen in the exhaust manifold by sending a signal voltage (0.1V to 0.9V) to the PCM.

This heated oxygen sensor sends a small voltage (towards 0.9V) if the fuel ratio is rich. But, if the air fuel ratio runs lean, it will generate an even smaller voltage (towards 0.1 V). The control module correlates these voltage signals with the oxygen in the exhaust to manage the air fuel ratio (fuel trim).

When the Bank 1 sensor takes longer than expected to warm up, or if the upstream sensor isn’t reading the amount of oxygen in the exhaust, the PCM takes it as “no activity detected.”

As a result, the PCM activates the Check Engine Light and registers code P0134.

Note: Some Japanese vehicles use an air fuel ratio sensor or AF sensor instead of a conventional oxygen sensor to measure the ratio between fuel and air in the exhaust stream. The air fuel ratio sensor is not interchangeable with a conventional oxygen sensor. 

Common symptoms

A fault in the upstream O2 sensor or its sensor circuit could lead to several symptoms, including:

• Illuminated check engine light
• Misfiring
• Engine hesitation on acceleration
• Rough idle
• Poor fuel economy
• Excessive smoke from the exhaust 
• Failed emissions test due to excessive exhaust gas

Note: If your PCM registers another code along with P0134, the symptoms may differ from those listed here. Also, some vehicle owners may not notice any signs other than an illuminated engine light, but that’s a rare occurrence.

Can I still drive?

The P0134 code will not cause any immediate drivability problems, but you may experience low engine power.

That said, code P0134 is still a moderately severe issue as it could lead to your engine consuming more fuel. Not only will this lead to a drop in fuel economy, but it can also damage the critical components of your engine, such as the catalytic converter.

So, driving with this Bank 1 sensor engine code for a prolonged period is not recommended, and you should get the code diagnosed and resolved as soon as possible.

P0134 causes

Whether you own a Honda Motor Company vehicle or a Nissan, several potential causes could lead to your PCM registering fault code P0134. Sometimes, it could be a faulty air fuel ratio sensor or a damaged harness connector. 

Here are the common root causes for this check engine code:

• A bad O2 sensor
• Short or open O2 sensor heater circuit
• Poor connection at the O2 sensor connector
• Bad oxygen sensor ground
• Damaged sensor parts, such as harness connector or wiring
• Vacuum leak or exhaust leak
• Faulty fuel pump
• A faulty powertrain control module 

Diagnosis

Diagnosing this oxygen sensor code requires specialized knowledge and tools. 

Here’s how a certified mechanic will diagnose code P0134:

• Verify the trouble code: They’ll use an OBDII scan tool to verify that DTC P0134 is the only code present. If the PCM has registered any other code, they’ll fix it first. They’ll clear the code and take a test drive to see if the oxygen sensor code returns.
• Do a visual inspection: Next, they’ll examine the electrical O2 sensor connector, wiring harness, and the metal tabs of the heated oxygen sensor for any damage that could affect the sensor circuit. They’ll replace the damaged wiring or connector as required.
• Check the sensor voltage: If they don’t spot any physical damage, they’ll use a multimeter to check if the heated oxygen sensor is getting battery voltage. They’ll check if the sensor voltage varies between 0.1-0.9V when the engine runs at operating temperature. If not, they’ll suggest replacing the bad O2 sensor.
• Check for continuity: If they find the desired voltage at the O2 sensor, they’ll run a continuity test on the two ends of the sensor’s wiring. This wiring will run from the O2 sensor to a corresponding pin on the vehicle’s PCM.
• Check for exhaust and vacuum leaks: If the check engine light comes back again after replacing the faulty oxygen sensor, they’ll inspect the exhaust pipe for any signs of cracks or disconnections. They’ll also check for low fuel pressure by examining the fuel injector, fuel pump, and other parts that control the fuel pressure.

If the trouble code persists, they’ll check if the powertrain control module is at fault.

Possible repairs for P0134 & Costs

When it comes to fixing the DTC P0134 code, one or more of the below repairs can help resolve the issue:

• Replacing the bad oxygen sensor 
• Fixing an exhaust leak 

Repair costs

Here are the average repair cost estimates for the P0134 oxygen sensor code:

• Oxygen sensor replacement: $200-$300
• Exhaust leak repair: $100-$200 (if welded to repair)