P0136: O2 Sensor Circuit Low Voltage (B1S2)

What does the code P0136 mean? It’s one of the most common issues associated with a lit check engine light. Fortunately, it’s something you can fix yourself with the right tools and knowledge.

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What Are Common Symptoms?

Many times, a P0136 error code will only cause a lit check engine signal; you may not notice any performance problems at all. However, your vehicle may exhibit the following symptoms as well:

  • Misfiring
  • Exhaust leaks
  • Poor fuel economy

What Does the Code Mean?

What does it mean when you get an OBD-II scanner code P0136? It has to do with the voltage in your O2 sensor.

In order to properly monitor O2 levels in the engine, your sensor needs to be adequately powered. Too little voltage means the part doesn’t have enough power to consistently function. Too much voltage can cause components to overheat and potentially suffer damage.

A P0136 B1S2 means that the sensor located behind the catalytic converter is having this problem. When one O2 sensor is sidelined, the burden is divided among the others, causing all of them to work harder. The check engine light goes on when the system realizes there’s an issue with voltage, but the other symptoms are a consequence of less efficient O2 monitoring.

How Serious Is P0136?

This type of trouble is moderately serious, meaning that your vehicle should still be capable of running, but you risk major damage to your engine if you don’t address the problem as soon as possible. O2 sensors play an essential role in keeping your engine in prime condition; they monitor the ratio of fuel to air and signal the system to inject more or less fuel to keep the ratio ideal.

While other sensors pick up the slack when one malfunctions, this isn’t a sustainable solution. Eventually, the air-to-fuel ratio may be affected, leading to serious performance problems and possible damage.

What Causes Error P0136?

This error can be caused by a number of factors which may vary by make and model. For this reason, it’s a good idea to check for any recent service bulletins released by the manufacturer. If there aren’t any service bulletins, the cause may be one of the following:

  • Catalyst failure
  • Exhaust leak
  • Faulty oxygen sensor
  • Damage or corrosion on connector
  • Short in signal circuit
  • Air intake system leak

How to Fix P0136

With so many possible causes, you may be wondering, “How do I fix trouble code P0136?” The key is to inspect the system thoroughly, starting with the O2 sensor.

The first step is to verify the circuit voltage yourself to see if it’s actually outside specifications. If the voltage is fine, the issue may be the sensor. When a sensor is broken or dirty, it may not be able to function properly. You can clean or replace one fairly simply. If there is an issue with the voltage, it’s time to examine the circuit.

Inspect the wiring and connectors. There may be damage or corrosion causing the circuit to open.

Replace any components that aren’t up to par. You should also look at the heater circuit to check for any issues there.

If the O2 sensor and circuit are in good condition, check for any exhaust leaks. If you can’t find any leaks, give the catalyst converter a thorough inspection to see if there’s any damage or corrosion.

A OBD-II scanner error code P0136 problem is something you can remedy in your own garage if you have the patience to examine the system. Most times, the trouble is with the sensor or circuit, but don’t fall into the trap of just replacing the sensor and thinking you’re done. Remember that if the issue isn’t solved correctly and there was a more elusive cause, you could end up paying for it later. You can get the parts you need at your local AutoZone Store. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

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Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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