Oxygen Sensor Replacement

Contour Enthusiasts Group Archives

Car Info 1996 SE V6 2.5L 110K Miles.

I'm going to change my O2 Sensors this weekend when the weather gets better so I am trying to find out more information about replacing them.

Anyway, my question is that from reading through the threads, I understand there are 4 oxygen sensors. Of which I located the first oxygen sensor Upstream Bank 1 O2 Sensor Replacement

My question is where are the other 3? Can someone illustrate the locations to me?

Other question is I went to autozone and the codes I pulled are P1131, and P1151. The guy told me my car only has 2x O2 sensors therefore only sold me 2. Should I go back and buy another 2? or just replace 2 of them?

The downstream sensors long outlast their rated life (only thing on the car).

The upstream sensors are on the exhaust manifolds. One in front (bank 2), one in back (bank 1). The one in front is under the plastic cover.

My downstream failed at 57000 they dont last very long.

okay, so for my code P1131 and P1151 should I replace the upstream sensors with the Bosch 13115 on bank 1 and bank 2? Does anyone know the return policy of Advance Auto? I probably need to change the Downstream Sensor for the UpStream to make a set of two upstreams.

Someone please confirm with me. Thanks!!

P1131 and P1151 are lean codes for banks 1 & 2.

This can be the upstream sensors going out (over about 80k miles) since the upstream sensors control fuel trim.

These codes can also be caused by low fuel pressure, dirty MAF, vacuum leaks...

At 110k miles, I would go ahead and replace the upstreams if they are original.

There should be no reason to replace the downstream sensors. They only alert the computer if they sense CAT problems. They do not affect engine operation and rarely go bad because they stay clean behind the CATs.

Most places will accept full return if merchandise is unused.

If these 1131/1151 codes are concurrent, I would look to other things before changing both of these sensors. Changing these out is not easy work. At 110k, sure it is not a bad idea to change them but it may be something else that is causing them to trip the CEL.

If you have located bank 1, sensor 1, bank 2 sensor 1 is in the same location on the opposite bank .... ie somewhere below the top of the rad. Sensor 2 on both banks can be found at the bottom of the respective precats. They are easily seen while under the car.

MarkO,

since it can be seen easily under the car, would you recommend me to change the sensor from underneath or still from the top?

I do have access to a car lift but I do need to ask the permission of the owner if working from below is the easiest.

Btw, I went by Advanced Auto and they looked at me strange when I told them I needed to replace the downstream for a second bosch upstream sensor. He told me in his life he has never seen a car needing two identical upstream sensors.

I meant to address this to anyone else too if they can help me instead of just MarkO.

Thanks

Quote:

since it can be seen easily under the car, would you recommend me to change the sensor from underneath or still from the top?

I do have access to a car lift but I do need to ask the permission of the owner if working from below is the easiest.

Btw, I went by Advanced Auto and they looked at me strange when I told them I needed to replace the downstream for a second bosch upstream sensor. He told me in his life he has never seen a car needing two identical upstream sensors.

I replaced the bank 1 sensor from the top. You may want to remove the plugs from the coil pack and a wiring harness in order to get a decent space to manuever your arm. Also, perhaps some liquid wrench if the sensors are TIGHT.

Originally posted by GreatGonzo:
I meant to address this to anyone else too if they can help me instead of just MarkO.

Hey, I gotta sleep and work too .....

The lower sensors are most easily changed from under the car. Put the car on ramps. Crawl underneath and look at the y-pipe. Follow it back on either side and locate the sensors. Change them if you want to.

The bank 1 sensor 1 is awkward to change because of its location (under the coilpack). Pull the coilpack off, move the hard wiring harness as best you can and use a long handled 7/8" wrench to loosen the sensor from the manifold. You may be able to get the sensor all the way out from up top but I wasn't. I got under the car again and reached up and located the sensor with my fingers. (You'll be doing it by feel) Then I loosened the sensor the last couple of turns and out it came. Disconnect the plug from the wiring harness. I installed the new sensor the same way, I got it threaded from underneath and tightened it from up top. It helps to have long arms. Dont do this while the car is warm or you'll burn your arm on the manifold.

I haven't changed the bank 2 sensor 1 O2 sensor so I have no knowledge of what needs to be moved out of the way to gain access.

The front upper sensor is a piece of cake. If you can't find it, you should give up and take the car to a shop. Removing that plastic cover helps to see it from the top.

Steve

Two years ago, I did both upstream sensors on Mom's Mystique, so I anticipated the pain for doing the Bank 1 #1 sensor on my car today. It took me 3 1/2 hours, plucking out the wiring to the PCM, severing the pigtail to the sensor, a 22mm wrench and a 5-inch crescent wrench before I got the car back up to snuff. How the heck do the mechanics do it?

AND make any money?

BTW: Can an O2 sensor go bad for years before the PCM tumbles on to it? When I fired up the car, the rotten egg smell was all gone, but it been there since early '03... and the CEL had been on for only 2 weeks.

I used a low profile O2 sensor socket that work out pretty good on bank 1 and bank 2 sensors,BTw did anyone have all the 02 sensors pictures? I really can't find any sensors other than the two I had replaced.

Originally posted by April Thompson:
BTW: Can an O2 sensor go bad for years before the PCM tumbles on to it?

Yes. The O2 sensor degrades in a linear, analog manner, slowly getting worse as time goes on.

The PCM, however, considers the O2 sensor to be in either one of two states: "good" or "bad"--which it isn't.

It's like shades of grey vs. black and white.

I got a fun thing now: throttle hang. I change the sensor, now the engine runs for a second at 2000 RPMs, then drops to 1250 for half a minute before settling at AROUND 1000. Before, I would start up and it would waffle a bit before sticking at 750, but feel sluggish at low RPMs, even with functioning butterflies. Now, it's so eager to rock, it revs into action straining at the end of its leash. Sigh. Can't win for losing sometimes...

Originally posted by zzzcool:
I used a low profile O2 sensor socket that work out pretty good on bank 1 and bank 2 sensors,BTw did anyone have all the 02 sensors pictures? I really can't find any sensors other than the two I had replaced.

They're in the Y-pipe on V-6 models: Bank 2's is actually quite visible near the oil pan. Bank 1's is just above the bend of the pipe, where it fits to the manifold. PITA to reach, quel surprise. Follow the leads with bright blue connectors, if all else fails.

The bright blue connectors are for the downstream/post cat sensors. The upstream sensors are going to be probably 5" above them.

Disconnect the battery for a few minutes--see if that fixes the throttle hang.

If not, maybe try cleaning the throttle body.

I want to get all the intake gaskets, as well as the TB, IAC and misc. gaskets so I can clean them all at once. But, yeah, the TB is filthy.