P0136 – O2 Sensor Circuit

The OBD2 error P0136 code triggers when your downstream oxygen sensor’s voltage drops below the minimum threshold for too long. This means your air-to-fuel mixture is too low, which can have serious consequences for your engine.

Often, the symptoms of this code are mild. Don’t let that deceive you into ignoring your check engine light. While driving with the P0136 trouble code isn’t dangerous, it could lead to misfires and other engine problems.

The good news is, the P0136 code is usually easy to diagnose. Following the correct steps will let you fix the issue efficiently, without making any unnecessary repairs.

P0136 Code Definition

P0136 Code Definition (Generic): Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)

P0136 Ford Code Definition: (O2) Circuit (Bank 1, Sensor 2)

P0136 Toyota Code Definition: HO2S-12 (Bank 1 Sensor 2) Circuit Malfunction

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What Does P0136 Mean?

The computer in your engine monitors the oxygen sensors to ensure they’re operating properly. This includes measuring the maximum and minimum voltage levels produced to make sure they’re within specified parameters. 

The oxygen sensor voltage helps your powertrain control module (PCM) or engine control module (ECM) to track the air-to-fuel ratio. If the voltage is too high, the mix is rich. A low voltage indicates a lean mixture. 

In response to a high or low voltage, the ECM or PCM will adjust the air/fuel mixture. When this doesn’t change the sensor reading after a designated length of time, the P0136 trouble code is triggered. P0136 refers specifically to the downstream oxygen sensor, called sensor 2. It is very similar to the trouble code P0137.

The specific voltage and time threshold can vary depending on your vehicle. Similarly, you may want to follow different repair steps specific to your make and model, even though this is a generic powertrain code. Check your vehicle’s manual, and search for any technical service bulletins for your vehicle before beginning your repair. 

What Are The Symptoms Of The P0136 Code?

There may be no drivability symptoms with the P0136 trouble code. If there are, they typically include one or more of the following: 

  • Activation of the check engine light
  • Reduced fuel economy
  • Reduced engine power
  • Misfires due to lean engine condition

What Are The Causes Of P0136?

  • Exhaust leaks
  • Faulty oxygen sensor
  • Opens or shorts in the oxygen sensor signal circuit
  • Clogged, damaged, or faulty catalytic converter
  • Damaged or faulty wires and connectors on the oxygen sensor

How Serious Is The P0136 Code?

The P0136 trouble code is of moderate severity. You can drive for a short while with this code active. Extended operation with a lean condition can lead to internal engine damage, however. Even if the symptoms aren’t severe, you should take your vehicle for repair as soon as possible

How To Diagnose And Fix The P0136 Code

OBD2 scan tool is one of the tools to diagnose the P0136 code
Just need a few operations with OBD2 scanner, user can diagnose the P0136 code.

Tools you’ll need:

  1.  Use an OBD2 scanner to check for other trouble codes and read the freeze frame data to see the conditions under which the code was set. Next, clear the codes and test drive your vehicle. If the code returns, continue with your diagnosis.
  2. Check for leaks in the hoses, catalytic converter, and other exhaust components ahead of the oxygen sensor. Make sure you feel for damage and leaks in hidden areas. Pay close attention to the ends, checking that they’re not frayed and firmly connected. 
  3. Read the live data from both oxygen sensors and compare the readings. They should change in tandem with each other. If the downstream oxygen sensor’s voltage is fluctuating quickly compared to the upstream sensor, you likely have a wiring issue or faulty oxygen sensor.
  4. Visually inspect all the connectors and wires around the oxygen sensor. If there is corrosion on the connectors, you can often clean it using MAF cleaner.
  5. Inspect the oxygen sensor for evidence of damage. If it’s contaminated by coolant, oil, or other engine fluids, be sure to check for leaks elsewhere in the system. Clean or replace the oxygen sensor as necessary, then clear the codes and test drive your vehicle to see if the P0136 trouble code returns.
  6. Test the oxygen sensor using a digital multimeter, even if there’s no visible evidence of damage. The sensor may have internal short or other faults. Warm up your engine, then connect the positive lead to the oxygen sensor. Connect the negative multimeter lead to your negative battery terminal or a ground point on the chassis. The reading should fluctuate. If it’s steady at around 5 volts, the sensor is faulty and should be replaced.
  7. Use the multimeter to test the ground wire for an open or short. If it’s functioning correctly, test the wires running from the wiring harness. Failure of two or more wires likely means you should replace the entire wiring harness.
  8. A clogged catalytic converter can cause a lean air-to-fuel ratio. Taking a hard drive can often clear blockages. Take your vehicle on the highway and drive above 55 miles per hour for at least 15 minutes, then drop quickly to a lower speed. 
  9. If the code still doesn’t clear, take your vehicle to a mechanic for further diagnosis. You may have a more serious issue with your catalytic converter or exhaust system that they’ll be able to identify with pinpoint tests. 

Common Mistakes To Avoid While Diagnosing The P0136 Code

Many mechanics automatically replace the oxygen sensor when this trouble code triggers. While this may be the issue, you should check for leaks and wiring issues before replacing any components. This could save you money and effort, and ensures you fully resolve the problem. 

Tips To Avoid P0136 In The Future

Corrosion and other damages on the wires and connectors are one main cause of the P0136 trouble code. Preventative maintenance can reduce wear to wires. Ensure no wires are rubbing anything that could cause shorts or damage. You can also treat your engine block with an anti-corrosive agent to extend the life of electrical components.

Read more: P0132 Code – O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)