Hello there everybody. I own a 2005 Honda Civic DX with approx. 52000 KM. I recently got a check engine light code registering P0139. However, this is not what has gotten me on this forum. When I went to Autovalue to get the code, the gentleman that did it for me asked if I would like to turn off the check engine light. I said yes. Now, it's been at least 2 or 3 weeks and the light has not come on so I guess my question is, should I worry about the light coming on anymore or is it fine since it has not come on since I last turned it off?

Thanks to everyone in advance for their response!

 

Well, congratulation, your secondary O2 sensor is out. I just ran into this problem last weekend, and being rip off $250 + labor. But far as I know, the factory OEM part is your best bet. Since after market part will not last long.
Happy money burning season...
But if you can clear the code and not come back, I think you are good for quite a while. O2 sensor is not a must have component for the car anyway. You can live without it. I am figuring by pass the sensor when my new sensor is gone.

 

O2 sensor(s) is needed for proper running of engine so the engine will have proper AF mixture. Manufacturer did not install for "no reason".

 

Well, I am not sure about Civic's engine. But I know some ECUs determine the FA ratio by using the MAP value and refer the Air Temp for compensation. The O2 sensor is just part of self-diagnose system, some people actually bypass them when they do the exhaust modification.

 

After 1996, there are two sensors. The first sensor (before the catalytic converter) is essential to fine tune the A/F ratio. The second sensor (after converter) is used only to check the operation of the converter. If that sensor is faulty, CEL will come on but engine will still run OK.

If you do "exhaust modifications" that involve removing the catalytic converter, you get no love from me since I prefer not to breathe polluted air. Also it is illegal under US federal law to do that to any car that will be used on public roads. It's at least a $25,000 fine even in areas that do not require a smog test.

 

I found this and was wondering if I could just leave it since the CEL did not come on after I reset it...

[P0139 OBD-II Trouble Code

Technical Description

Oxygen Sensor Circuit Slow Response (Bank1, Sensor2)

What does that mean?

This involves the rear oxygen sensor on the driver's side. This code indicates the engine air fuel ratio is not being adjusted by the oxygen sensor signal or the ECM as expected to do so, or not adjusted as often as expected to do so once the engine is warmed or under normal engine use.

Symptoms

You will likely not notice any drivability problems, although there may be symptoms.

Causes

A code P0139 may mean that one or more of the following has happened:

The oxygen sensor is faulty
The wiring to the sensor is broken / frayed
There is an exhaust leak
Possible Solutions

The simplest thing to do is to reset the code and see if it comes back.

If the code comes back, the problem is more than likely the rear driver's side oxygen sensor. You will likely wind up replacing it but you should also consider these possible solutions:

Check and fix any exhaust leaks
Check for wiring problems (shorted, frayed wires)
Check the frequency and amplitude of the oxygen sensor (advanced)
Check for a deteriorating / contaminated oxygen sensor, replace if necessary
Check for inlet air leaks
Check the MAF sensor for proper operation]

Thank you to everyone for your reply's! They are much appreciated!

 

So what your saying is if my check engine light comes back on after replacing my upstream o2 sensor, then i may need to replace my secondary o2 after the cat???

 

I will recommend you use a code reader to check which one went before you do anything. It is a good way to save money and time.