O2 sensors.. How hard can it be?

I'm 'chanelling' Jeremy from Top Gear when he says 'How hard can it be...' and of course - something blows up or crashes right after he says this. I've got two codes; P0130 and P0150 and both are the O2 sensors ahead of the cats. I've had it before - last spring and cleared the CEL and it didn't come back until yesterday. Reading up on these things it says expect them to go bad with high mileage and sometimes they get dirty and the signals to the ECU slow down to the point where the system 'guesses' on fuel/air settings. I've have had warm up issues with the RPM hunting around until the temps come up and have been living with it. The codes say it looks like it runs too rich. I've cleared the codes so we'll see what happens in a few days but I know this issue is going to come back, so... I'll most likely replace both of them. 'How hard can it be'? Will I find these things screwed in so tight after the car has gone over 100Km's that I won't be able to budge them? Risk of snapping one off? I've seen a special socket or wrench - a 22M - that you can buy. Isn't there enough room for a normal 22M wrench? The Bosch part at Pelican is $124.00 each. A bit pricy but it is what it is and if they have lasted this long then it's not bad value I guess. If I get the rear of the car off the ground is this a slide under and reach up DIY or do I need to rent time on a hoist?

Both of them reading bad at the same time suggests that the problem may be upstream. I'd try to clean the MAF first. I once went through replacing O2 sensors in a 4runner only to find out it was the MAF throwning off the amount of fuel being injected resulting in a bad reading at the O2 sensor. If one sensor was doing this on it's own it would be another story.

I just had my cats off my car. It will take you about 15 minutes to remove the back bumper. You do not need to jack the car up. Apply a liberal amount of penetrating oil to the O2 sensor/exhaust bung. You might be able to remove the O2 sensors with the bumper in place, but it sure does make getting to them way easier.

The special socket will have clearence (slot or...) for the wires.

Mark...what kind of cats are those? My OEMs don't look like that...

Take off the cat sections and save yourself a lot of grief. A little PB Blaster, and you're all set. Make sure to label your pre- and post- cat wires before you unplug them More Pics

The plugs and sockets for the pre and post O2 sensors are different, so you can reverse the wires.

Thanks for all the tip's guys. I'll try the 'easy' fix first - cleaning the MAF. No harm no foul if it doesn't work, right? <Well unless I drown the thing in too much fluid it can't hurt!> One quick question. Do I use anti-seize on the O2 new threads? <I know, less is more>

hopefully its not your cats.....

Personally, I use a little anti-seize on O2 sensors. Not that it'll last - it'll get burned off, but giving the threads a little lubrication to start is a good thing.

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Connector terminals are different color between pre and post (grey and black, I think). So as long as you match the color you will be good. Rick 99 996C4 87 944S

I did use a little anti-seize; see pics. If your cats are bad; I have a spare OEM set; PM me if needed. And re: plugs; they look the same to me, except for the color of course. It was my first time messing with them, so I labeled to be the extra safe

Sean, they are a custom made set that I bought used. I believe the converters are Magnaflow. They weigh about 1/2 stock and sound fantastic.

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Wouldn't I have a failure of the downstream O2's - after the cat's? The codes I'm getting are for the O2's ahead of the cats. I find it suspicious that both sensors fail at the exact same time. It if were age related... it doesn't make sense. The real time volt numbers were both going up and down depending on the RPM I was putting into the car. Each bank sensor would go off scale 0 and then increase to say 0.9V as I rev'ed the car. They were not exactly the same volts each at any given point but it appeared that they were working somewhat. I can't tell if the signal is getting to the ECM in the correct way or amount of time for it to make proper adjustments to the fuel/air mixtures but I'm now leaning towards the suggestion of cleaning the MAF first and driving it after to see what happens. I will get to it next week as I'm at the track this weekend so it will have to sit in the garage until I get back on Monday.

I took one of the O2 sensors off mine with just an open end wrench. Just bump the wrench with your hand like an impact wrench and as long as it doesn't slip, it shouldn't be that hard to remove. Mine had over 100k miles at the time so if it was going to be stuck in there, it was then. I didn't remove any parts to get to it except the airbox. The hardest thing for me was snaking the wires in and out the proper way.

UPDATE: Cleaned the MAF today and also found rubber oil ring seal on inside of oil fill cap out of position. Cleared codes and went on a drive twice today and NO codes in ECU and No CEL. So it was either a dirty MAF or an air leak through the oil cap, (or both). Tah Dah!

You should not use penetrating oil around the sensors. They won't be that tight unless they were installed incorrectly. If you want to use penetrating oil be sure to thoroughly clean the area where you applied it to remove all traces of this stuff. If any remains it can ruin the new sensors. Applying to any old sensors ruins them even if they would have been otherwise ok. Sincerely, Macster.

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I used electronic cleaner, I use it on my circuit boards at work worth $80K a pop - safe for MAF. No residue left behind.