O2 sensor on 2000 24v

Hi,
I was hoping someone could shed some light on this subject. My 2000 duratek check engine light is coming on and reporting that the o2 sensor in bank 2 is "below threshold". I replaced it about two weeks ago, reset the code and all was fine for a few days and it came back on. The code came back the same. I just had it reset again with no further actions. After that I took a 250 mile round trip drive and the light never came on and all was fine. Then today on the way to work it came on again, I am pretty certain it is going to read the same fault code again. What would be a good place to start now? Is the new o2 sensor faulty already?

The car runs fine, plenty of power etc. Other than the crappy fuel milage but that has always been the case since I bought the car 2.5 years ago. Just for verification on the o2 banks. Is bank #1 closest to the radiator and bank #2 closest to the cat? The o2 sensor I changed was closet to the cat. TIA.

Welcome to the forum!

It appears you fell for the common misconception that a diagnostic code points to the part that is bad. That's not always the case, the code just points to the system that has detected a problem. Many things can cause an abnormal reading on the oxygen sensors. If you provide the precise code number in the format P0123, we'll be able to provide you with some specific troubleshooting steps and areas of particular interest.

In addition to providing the precise code, once you have the code, please use the "Search this forum" feature from the Taurus forum main page to find the steps provided to and used by other forum users for that particular code.

On your V6 Taurus, Bank 1 is the bank nearest the firewall and Bank 2 is the bank near the radiator. The code would also indicate a sensor number, either 1 or 2. Sensor 1 is before the catalytic converter, sensor 2 is the sensor after the catalytic converter. The code should have something like "B1S2" in the description. In this example, the referenced sensor would be Bank 1, Sensor 2.

-Rod

Welcome to the forum!

It appears you fell for the common misconception that a diagnostic code points to the part that is bad. That's not always the case, the code just points to the system that has detected a problem. Many things can cause an abnormal reading on the oxygen sensors. If you provide the precise code number in the format P0123, we'll be able to provide you with some specific troubleshooting steps and areas of particular interest.

In addition to providing the precise code, once you have the code, please use the "Search this forum" feature from the Taurus forum main page to find the steps provided to and used by other forum users for that particular code.

On your V6 Taurus, Bank 1 is the bank nearest the firewall and Bank 2 is the bank near the radiator. The code would also indicate a sensor number, either 1 or 2. Sensor 1 is before the catalytic converter, sensor 2 is the sensor after the catalytic converter. The code should have something like "B1S2" in the description. In this example, the referenced sensor would be Bank 1, Sensor 2.

-Rod

Thanks for the reply. I am going to stop by the auto store on the way home to get it read again. If I remember correctly the code was 430, I will search it out on the forum. According to your description of where the banks are located, I think I may have replaced the wrong one, I replaced the one closest to the firewall and cat, and not the one closest to the front of the car. But the display on the code reader did specify bank #2, that for some reason stood out the most to me.

I did go and get it checked again and it was po430. I also swapped around the sensors because I had the banks mixed up as to which was which. Gonna give a day or two and see what happens. Hopefully this will take care of my 13mpg I have been getting since I owned the car.

I doubt the O2 sensor will have that large of an impact on fuel economy. Are you using a stock paper air filter, or do you have a "performance" oiled air filter? Either way I'd suggest you clean the MAF sensor, but I'd almost place money on it having a significant impact on fuel economy if you are running an oiled filter.

Again, diagnostic codes do not necessarily state the part that is the culprit, but rather the part/system that is detecting on out of specification condition. I review the contributing areas for a P0430 tonight and post back.

-Rod

It is just a standard air filter.

A bad pre cat 02 sensor can make a huge difference in fuel economy! If indeed that is the only problem.

The P0430 code indicates Bank 2 catalyst system efficiency is below the acceptable threshold. The code by itself would indicate a potential problem with the catalytic converter, not necessarily the oxygen sensor.

According to the factory service manual, possible causes are:

Use of leaded fuel
Damaged HO2S
Malfunctioning ECT
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires improperly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timingOne way to diagnose the real issue, again from the factory service manual, is to "Compare HO2S upstream and downstream switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increase amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set. "

-Rod

Ok, now this is odd. Things have been fine and today it was hot enough that I turned the AC on. After I did and few minutes later the check engine light came on. Now that I think about it, every time that I have turned the AC on, that is when the light would come on. And everytime that I go and check the code it reports O2 sensor bank #2. It seems to stay off until I use next use the AC. Any suggestions on this?

So you're still getting a code P0430? Again, that does not necessarily point to a bad O2 sensor, it is for Bank 2 catalyst efficiency.

When you turn the A/C on, the IAC should open further to compensate for the load the A/C compressor puts on the engine to maintain a constant idle speed. Maybe it is also increasing the injector pulse width, but too much and you're getting a rich condition, contributing to a catalyst efficiency concern due to too much fuel in the system.

-Rod

So you're still getting a code P0430? Again, that does not necessarily point to a bad O2 sensor, it is for Bank 2 catalyst efficiency.

When you turn the A/C on, the IAC should open further to compensate for the load the A/C compressor puts on the engine to maintain a constant idle speed. Maybe it is also increasing the injector pulse width, but too much and you're getting a rich condition, contributing to a catalyst efficiency concern due to too much fuel in the system.

-Rod

Yes, P0430 is back. I do think it is running rich as it is, this actually is starting to make sense I think. Could this be the reason for the 13mpg? Would my next step be to check the IAC?

I also had some work done on it at the dealer and asked them I wanted a computer analysis done, I never told them why I wanted it, but I was looking for a reason for the fuel mileage problem. When I asked them about it later they said it did not report any codes. So, I am assuming that all they did was plug the scanner in. When I said I wanted a computer analysis I was expecting them hooking it up to a real computer and really probe the system. Did I ask for the wrong thing or what or did they take the easy way out. Nevertheless I was never charged for that. So, I am not upset about it, just aggravated they may not have given me what I asked for. If it found the problem it would have been well worth the expense.

Sure, 13 mpg would certainly indicate a rich condition. I would not expect the IAC to be the culprit though as it only really has an impact when the engine is at idle. You may find that cleaning the MAF sensor helps out the poor fuel economy and possibly even helps the codes.

Have you tried searching this forum for "P0430" to see what others have found to be the culprit? You should try that.

As for the code scan, you'll probably have a difficult time getting a full analysis performed by a shop. That takes time and it will be expensive. That process would typically only be explored when looking for a specific problem since knowing the symptoms will limit the paths that the technician would need to analyze. There is a lot of information available from the PCM and it's not a simple task to record all the information, print it out and compare it against "go/no go" values. What you will want to ask for in the future for such information would be to request all the "CID and PID values with addresses." That still won't give you all the parameters available, but will be a good start.

-Rod

Ok, now this is odd. Things have been fine and today it was hot enough that I turned the AC on. After I did and few minutes later the check engine light came on. Now that I think about it, every time that I have turned the AC on, that is when the light would come on. And everytime that I go and check the code it reports O2 sensor bank #2. It seems to stay off until I use next use the AC. Any suggestions on this?