The OBDII code P0139 is a warning that the vehicle’s engine management system has detected a problem with the O2 sensor. Honda Accords can display the OBDII code P0139. During voltage level switching, a delay in the oxygen (O2) sensor’s response time triggers the code.
In order to create the optimal air/fuel mixture, oxygen sensors assist the ECM in measuring oxygen levels in the exhaust. The ECM can no longer manage a mixture if they fail to respond in a timely manner. It is also possible for P0139 to be caused by less likely problems. Below, we’ll take a look at them.
P0139 Honda Accord Definition: O2 Sensor Slow Response (Bank 1 -Sensor 2)
Bank 1 refers to the side of the engine with cylinder 1 in the firing order. Engine Control Modules (ECMs) set the P0139 code when rear O2 sensors take longer to respond between rich and lean than specified.
The ECM will go into diagnostic mode, where it will look at all of its sensors to see if they are functioning correctly. If no other codes are set, then this means that there is a problem with your rear O2 sensor.
Common Causes of P0139 Honda Accord
The Honda Accord’s P0139 code is caused by the following issues most commonly. We have arranged them as far as most likely to cause the problem to least likely to cause the problem.
A Wrong O2 Sensor Has Been Installed
The Oxygen sensor may have been replaced incorrectly if you get P0139 after having recently replaced it.
There Has Been Damage To The Terminal
In addition to the oxygen sensor, the plug that connects it to the oxygen sensor is fairly susceptible to damage. Ensure that there is voltage flowing to it. Here’s more on that.
Issues With Wiring Harnesses
It is easy for the wiring to be damaged that runs to the oxygen sensors in the front and rear to. In addition, despite being under the chassis, O2 sensors suffer from damage from road debris due to their location.
The exhaust heat is also a problem. There is a particular risk associated with the downstream sensor.
Oxygen Sensor Malfunction
O2 sensors themselves are most likely to trigger the service engine soon to light associated with P0139. It would be good to check out the wiring harness surrounding it before replacing it, even if it is a temptation to do so right away.
Some Other Possible Causes Of Code P0139 Honda
- Pressure in the fuel system is incorrect
- The fuel injectors are faulty
- There may be a problem with the intake air leak
- Leaks in the exhaust system
Symptoms of Honda Accord P0139
It is common for the service engine soon light to be the only sign of P0139. However, other symptoms may also be present in some cases. Symptoms such as these include:
- An increase in emissions
- Exhaust smells bad
- The service light has come on
- Trying to ping
Because of the higher levels of pollutants in the exhaust, vehicles with P0139 often don’t pass emissions tests. Therefore, the sensor should be working properly and not the cause of the error code.
Diagnosis of Honda Accord P0139 Trouble Code
P0139 can be diagnosed with a multimeter. A multimeter can tell you whether the voltage coming to and from the oxygen sensor is within specification, which can help you determine whether the problem is with the O2 sensor or the wiring harness.
The wiring between the fuse box and the oxygen sensor should be checked first if you do not have access to a multimeter. Buying an unnecessary O2 sensor will save you money if it turns out to be a wiring issue. Voltage test lights (available for around $5 at Walmart) can also be used to check the oxygen sensor.
You can try shaking the wiring once the test light is attached to the harness plug if it isn’t getting any voltage. The P0139 trouble code indicates a short circuit when you see the light come on for even a second.
Troubleshooting The P0139 HO2S-12 (Bank 1 Sensor 2) Circuit Slow Response Honda Accord
There is a problem with the rear oxygen sensor that does not properly read oxygen content and adjusts the air/fuel ratio as expected.
There are several possible causes of this, including a malfunctioning sensor, damaged or broken wiring, or a leak in the exhaust system. If you would like to correct this, please check the following:
- Fix any leaks in the exhaust system
- Make sure there are no wiring problems (shorted or frayed wires)
- Test the oxygen sensor (advanced) for frequency and amplitude
- Replace an oxygen sensor if necessary if it is deteriorating or contaminated
- Make sure there are no leaks in the inlet air
- Make sure the MAF sensor is working properly
A qualified technician may be able to diagnose the trouble code and correct the issue at your location if you need some assistance with this.
The Honda P0139 code may be set in a number of situations. The rear O2 sensor can become fouled with carbon and no longer function properly.
Or the wiring to the sensor can break and cause an intermittent connection, or the sensor can malfunction. Replacing the rear O2 sensor is typically the first course of action, but other repairs may be necessary if the code continues to be set.