I have an 1997 Mountaineer AWD with the 5.0. The vehicle has 235,000 miles on it and has run great all this time. Early in the month the Check Eng light came on, I check the code and got "P0141 O2 Sensor Heater circuit Bank 1 Sensor 2". I check and found out it is the O2 sensor behind the Cat that is bad. I have never change any O2 sensor on this vehicle since I have got it brand New. I have changed the oil every 5000 miles and flushed out the trans every 50,000 miles. New plugs and wires at 100,000 miles. I take good care of my vehicle as best as I can.
My Questions are, should I go ahead and change all the O2 sensor's? Which brings me to ask. How many O2 sensors does this vehicle have and where?
Could it be something else causing the check eng light to come on?
How bad is it to change all the O2 sensors out?

Thanks for any help.

Tom

 

changing the sensor could solve the issue, after all its a sensor and sensors do go. As far as changing it, the post cat tend to be a pain in the butt to unscrew, at least mine was both times. As far as how many you have, that depends on your exhaust system, but it's gonna be either 3 or 4. You will have one on each bank pre cat and one after your cat.

 

Heater ckt code is almost always a sensor problem . Less likely a wiring problem . One sensor upstream both banks .That is two . One sensor post cat . Two cats ,? two post sensors . Total 4 . Ck layout of exaust . At least 3 ,possible 4 .

 

The answer is yes, you should replace all the O2 sensors. O2 sensors are good for about 100,000 miles or so. Anything beyond that is borrowed time, but more importantly, they loose accuracy beyond that point. If the sensors are no longer accurate, the computer cannot make good decisions in the fuel management, and economy, performance, and durability all suffer. Economy and performance are a given. Durability because carbon deposits will scuff the cylinder walls, trap heat in the cylinders, and cause all sorts of other mischief.

When I say replace all the sensors, I mean the upstream ones the ones in front of the cats. The downstream sensors do not need to be replaced unless they have a code particular to them. In your case, you do, so the offending sensor should be replaced as well.

 

That sounds like a good idea. Replacing the sensors will definitely help with overall quality in your Rigs effort and for the computer and general quality. And you are right KhanT.. The front 2 sensors are more important.. Going through my states required emissions testing and DEQ (Oregon), I found out about 1,000 miles ago my check engine light was on and the O2 sensor came up 'Slow to Respond' on the DEQ Report. So these sensors really throw everything off in these models. A normal price on this sensor at an Auto Parts store is around 45 dollars depending on where u live. But this is not always the exact answer to a chack engine light.. Just saying. But hope this stuff helps.

-Cam

 

That is true, sometimes the code is caused by damage to a wire or a loose or corroded connector. Even so, they are an often overlooked maintenance item that should be addressed.

 

Just an update, I replaced the Bad 02 sensor(right bank after the CAT). I also picked up the two front sensors to replace. The first one I replaced, right bank after the CAT was a pain to replug the connector. It was easy unscrewing the sensor and unplugging the connector. I unscrewed the front 02 sensor right bank but could not get my hand up to unplug it. It seats on top of the transmission. The left bank front 02 is very easy to get too.
Any advice on how to get up to the plug on top of the trans??? This Mountaineer has 4 02 sensors, 2 left bank and 2 right bank.

Thanks again

P.S.
the left bank 02 sensor after the CAT also seats on top of the trans. I am thinking of leaving it alone and only doing the front two.

 

I thought some Explorers had an access panel under the carpet.

 

Yes, on the 1997 Mountaineer, there is an access panel under the carpet and an console on top of the carpet. I tried taking out the console, but to much of a pain.