Replacing o2 sensors?

nadz · Post by **nadz** » 09 Apr 2011, 23:50

Hi,
Can anyone give me some detailed instructions on how to replace both o2 sensors? My car is a 1995 850 n/a. Pictures would be very helpful.
Thanks.

ratfink_v70_2000 · Post by **ratfink_v70_2000** » 10 Apr 2011, 03:52

All you need is an O2 socket. It has a cut out which allows it to slip over the wires then it's just a case of unscrewing like any other bolt/nut. At the other end is a plug and socket. Unplug old and plug in new.
Rich

VolvoTurbo850 · Post by **VolvoTurbo850** » 10 Apr 2011, 04:02

yes to that advice!

Keep in mind if yours is rusted on then it will be a real PITA to get it to budge. Also if the condition of the exhaust pipes are bad it could result in bending or splitting the pipe.

I often have my friendly neighbourhood exhaust guy do some of the work if it is not easy for me to do.

Post by **vjaneczko** » 10 Apr 2011, 08:34

Give them a squirt of PB Blaster the night before and then ten minutes before you tackle the job, it should go much easier. You might want to put a little anti-seize on them when you install them, too - you know, for next time

Post by **thecheat** » 10 Apr 2011, 08:37

First of all, get a torch and heat the bungs to cherry red, THEN use the o2 sensor socket. I broke a socket trying to remove my front one and was screwing around for over an hour with various tools before I dragged out the torch and had at it. Five minutes later it was backing out with a horrendous squealing noise!

I'm not sure if a plumber's torch will get it hot enough or not - supposedly there is a hotter gas than standard propane for the hand held torches.

You will need to make sure that there isn't oil in the wire strands of the old o2 sensor. If there is oil you have to get a harness from the dealer. What happens is that oil creeps into the strands and blocks airflow (the wires are channels for atmospheric air samples) and the sensor is ruined.

db130 · Post by **db130** » 11 Apr 2011, 21:00

i like to use a handheld mapp gas torch and the "crow's foot" type of o2 sensor tool. i've found that the slotted kind tends to flex more(i've cracked one in the past while trying to loosen a o2 sensor).

nadz · Post by **nadz** » 11 Apr 2011, 22:40

Thanks for the replies, but can someone explain this in a way for someone who knows nothing about cars, I don't even know where the o2 sensors are or how to access them.

Post by **jblackburn** » 11 Apr 2011, 22:47

First, you'll need ramps to get the nose of the car up in the air. The two sensors are on located on top of the catalytic converter - one at the front, one at the back.

Try the easy method first - I was able to get mine loose with a shot of PB Blaster 10 minutes before I started and one good whack on the socket wrench. If you can't get anything to happen with brute force alone after a few minutes, then it might be time to resort to the torch. My car is a Southern one and hasn't seen much road salt in its life, so there's very little rust anywhere underneath.

The harness for the connectors was the tricky part for me (mine being a turbo with stuff in the way; yours should be slightly easier). It's wedged in the back of the engine behind the transmission. You will have to remove the bracket holding them in from below, and then jump up top and pull the pink/red part away from the black plug part with a screwdriver. Then the plug should simply slide out, but separating the two halves required quite a bit of force.

Are you sure your O2 sensor is bad? 95% of O2-sensor related codes are from vacuum leaks somewhere in the engine bay; if you've eliminated those and are still having problems. then go ahead with the replacement.

nadz · Post by **nadz** » 20 Apr 2011, 20:55

jblackburn wrote:First, you'll need ramps to get the nose of the car up in the air. The two sensors are on located on top of the catalytic converter - one at the front, one at the back.

Try the easy method first - I was able to get mine loose with a shot of PB Blaster 10 minutes before I started and one good whack on the socket wrench. If you can't get anything to happen with brute force alone after a few minutes, then it might be time to resort to the torch. My car is a Southern one and hasn't seen much road salt in its life, so there's very little rust anywhere underneath.

The harness for the connectors was the tricky part for me (mine being a turbo with stuff in the way; yours should be slightly easier). It's wedged in the back of the engine behind the transmission. You will have to remove the bracket holding them in from below, and then jump up top and pull the pink/red part away from the black plug part with a screwdriver. Then the plug should simply slide out, but separating the two halves required quite a bit of force.

Are you sure your O2 sensor is bad? 95% of O2-sensor related codes are from vacuum leaks somewhere in the engine bay; if you've eliminated those and are still having problems. then go ahead with the replacement.

Not sure if the o2 senor is bad, but I bought the sensors a while ago anyway. I still need to install them, but how would you check for vacuum leaks? I don't even know what to look for or where they are located.

da7 · Post by **da7** » 20 Apr 2011, 22:20

hi jblackburn: I'm interested to know the same, is there anywhere on the net that lists out all the vacuum hose connections that is prone to break or leak (pictures would be good) or do we just have to go crazy with the propane and spray it everywhere?