Hey guys,

I have a 2000 Eddie Bauer Expidition with the 5.4. I ran my code reader and it popped up a P0156 code, meaning O2 sensor (bank 2 sensor 2). I am unsure which O2 sensor that is. How many O2 sensors on this beast (tried to decipher info on a search but with dial up it sucks) and would it be better to replace all of them? It has 75,000+ on it.

The gas mileage did drop about 4mpg and not running as smooth.

Thanks in advance.

Aaron
Nappers

 

It is the one after the cat on the drivers side. There are 4 HO2S (Heated oxygen sensors) on your vehicle. Two that are in the exhaust stream before the cats, which are used to monitor the air/fuel ratio and two that are after each cat, which measure their effectiveness.

 

The P0156 won't cause poor gas mileage, (HO2S2 is not used for fuel control) but the code can result from other conditions that do cause poor fuel economy.

If you have a misfire, address it first. It can cause excess fuel to be collected in the cat and keep the downstream O2 sensor from switching.

Other possible causes of a P0156:

An exhaust leak before the downstream sensor
Fault in wiring harness
Faulty sensor
Faulty PCM

Check your emissions warranty, some of these components are covered by your Federal warranty which, depending on where you live, could be an 8/80.

Replacing all four sensors would be a waste of money.

Steve

 

Thanks guys, I can see the O2 sensor through the wheel well, may see if a wire broke, didn't hear an exhaust leak but will check it out. It's got 75,000+ miles on it and may replace and reset light and see what happens.

Thanks again.

Aaron
Nappers