I have a '96 Ford Explorer and am thinking about replacing the O2 sensor. I've heard that it should be changed about as often as you change the air filter - once per year or so. Problem is, I have no idea where the O2 sensor is. My neighbor thinks the O2 sensor and the PCV valve are the same, but I don't believe so as I just replaced the PCV valve about a year ago. So, here's my question(s)...
Where is the O2 sensor located and how often should I replace it?
Also, how often should the PCV valve be replaced?
And, if any of these two items go bad, how significant is the effect on gas mileage?
Thanks
Webhead

 

Woah hold on a minute. 02 sensors are good for a lot longer than a year, unless you drive about 80,000 miles a year. My 02 sensors lasted 81K miles. No they are not the same as the PCV valve. And they are on the exhaust pipes. 4.0 have 3, V8's have 4. The 4.0 is on each downtube off the manifolds, and the 3 is by the cat. Not sure on the V8, but im sure its very similar. If your check engine light isnt on, you probably dont need new ones.

 

OH boy! Auto 101.

O2 sensor and PCV valve could not possible be at more different spectrums for engine control/management or even location for that matter.

Here's a link that you should read a couple times - each and every page - to help you understand you system. http://fordfuelinjection.com/

Now to your question. The PCV valve, as you know, is located in the valve cover, It does nothing more than allow the intake sytem to basically equalize the pressure inside the engine to the outside world - sort of. It allows the engine to pull gasses out of the valve cover - in essence the crankcase - into the intake manifold and burn the hydro carbons through the cylinders. Now, a vent to atmosphere would be OK to the engine. But CARB and the Feds dont like that - not to mention a few tree huggers - so it's now been redirected to the intake manifold where hopefully the CAT in the exhaust will kill any remaining bad guys from getting into the air. You need to replace this every once in a blue moon - more if you never change your engine oil - just so the crankcase can keep breathing OK. If you shake it up and down and nothing rattles -it is stuck and needs to be replaced.

O2 sensors are in your exhaust pipes. For a 96, you have 3. One of right bank, one on left bank - both before the Y where the banks come together - and the last after the CAT. Now these little gems are an electro-mechanical device that convert the presence of oxygen under a heated condition into electricity - kind of like a thermocouple, only different. So these bad boys tell the engine computer, or PCM, that the engine is running rich or lean. Don't ask me how. Some smart guy figured out that perfect 14.7:1 fuel mixture is .45 volts DC out of one of these things and so that is what the PCM targets. The PCM will add or subtract fuel to get a signal response from the O2 sensors of above, then below, then above, then below.... .45VDC for at least 3 of these switches per second. When the PCM gets such a response, it is very happy. When it don't it gets pissed and tells you in the form of a CEL light on the dash and a code stores in its memory.

So why change a O2 sensor? Well when they crap out. When do they crap out? Well that depends. How do we know? Well that depends too. And so Ford and other manufactures - thanks to CARB for your 96 and newer vehicles - you get OBD-II diagnostics on your cars. The computers, PCM's, will give you a whole host of codes to tell you when components are going bad - sort of. You get codes and then you need to decipher them. You never get a code that says -"go change right bank O2 sensor." It might say - O2 sensor right bank reading rich and not swithcing. Then you have to figure out why that is happening. Maybe the sensor is bad, maybe you have a leaking head gasket on the right side. Gets fun dont it?

So if you get CEL (check engine light) and can get the codes for why it came on, then you can start to diagnos the problem. Scanners are available cheap. I've seem OBD-II's at Aoutzone for $30 - plugs in under the dash, drivers side.

But then some people change O2 sensors as regular maintenance items - like spark plugs. Nothing wrong with that - fix it before it breaks. But at $45 a piece... So then "they" say every 60K-80K O2 sensors need to be replaced.

Gas mileage - Ah, such an important topic these days. Yeah a bad O2 sensor can cause you to loose gas mileage. But the PCM does try to compensate. The biggest deal here is that the PCM goes into a kind of limp mode of "open loop" operation where it ignores the O2 values and runs of a predermined set of air/fuel and spark curves that a engine safe - ie real rich - and that's what tanks 2-5 MPG, typically.

Lotsa info - hope it helps.

 

Great piece of advice there Jharger. I am dealing with the same problem on my 97 4.0 SOHC, so I will take a look at all these links and see what course of action I should take.

 

I just reached 125K on our '96 explorer, and the cel codes just told me that the bank 1 o2 sensor is responding slow. So they will last that long in a lot of instances. I would not change it on a regular basis, even though I have never had trouble changing one on friends vehicles, I have not been able to get my chubby little hands up between the trans dipstick tube and the engine block to undo the connector. Will the engineer that placed it there please respond with instructions on how to get it apart?

 

Replace on fails is always an option. And for O2's the sypmtoms ar quite obvious and most folks do just that. Maybe you get 20K or maybe 120K miles.

But lets think about this - the #1 input into EFI controls and we want to wait until the car just dies until we change it?

Hmm - I think I go with a regular, maintenance interval.

 

Just Received An O2 Sensor Code: "o2 Sensor B2 S1 Ckt Slow Response"
How Do I Know Which Sensor It Is And Where It Is Located?

 

Bank 2 is left side, drivers. 2003 X has 3 or 4 O2's from what I've heard depending upon 6 or 8 cylinder. Sensor 1 would be the one closest to the engine if there are 2 on tha side. Get underneath and find the sensors in the exhaust tubes. They got 4 wire connectors coming off them. The slow response is a OBD-II diagnostic code that says the PCM expected the sensor to switch from rich to lean to rich faster than it is actually doing. It's kind of a early warning sign of O2 failure - or some other issue but start with a new O2 firsts, disconnect you battery to clear the codes, run it and see if code comes back.

 

Thanks for your fast response. The explorer I have is a 1996 sport. Would the o2 sensor still be on the driver's side closest to the engine. The code is B2 S1.