Hello Everyone,

Thank you for your help. Between your advice and the pictures and text from Bay 13 I was able to successfully replace the front O2 sensor. I want to share some advice. After you install the new O2 sensor, you have to disconnect the battery for 10 to 15 minutes and then reconnect it. If you don't the Check Engine Light will remain on. I didn't the first time I started the engine. The Check Engine Light remained on and I thought I had failed. Of course, make sure you have the security code handy for your radio to be able to re-program it. When I disconneted the battery cable, waited 10 to 15 minutes and then reconnected the cable and started the car, the CEL went off.

Separately, I had an odd experience which I would welcome comments to. Based upon the pictures from Bay 13 both wire couplings for each O2 sensor (front & rear) are supposed to slide onto a metal bracket attached to the housing of the transmission which secures them. The bracket on my 850 (with a manual transmission) was missing. I went to my local Volvo dealer and confirmed such a bracket should have been on the car. I order one together with the screw you need to secure the bracket. I installed the bracket and put both O2 couplings on the bracket. It was a very tight fit for the front O2 sensor, there was barely enough slack in the cord to slip the coupling on the bracket. I suspect the bracket was removed on this car when the transmission was replaced under warranty by the prior owner. I suspected the technician when he put the transmission back in, didn't bother to re-install the bracket.

I then checked my other 1996 850 wagon, also with a manual transmission. It too was missing the bracket that both O2 couplings are supposed to slide on to. I was surprised, because I had purchased this car new and the transmission has never been replaced, though of course the O2 sensors have been over the years.

I asked my mechanic who worked in a Volvo dealership throughout the 90s and early 2000 when the 850 and subsequent V70 were introduced. He confirmed that these cars, even those with manual transmissions, all came with a bracket where you were to slide the O2 wire couplings on. My other '96 has the two O2 cables secured with wire fastners, so they are out of harms way and will not chafe against any surface. Still I'm surprised that both cars are missing the same bracket, which according to Volvo they should have. My mechanic did say the early O2 sensors failed alot and it was common when removing the couplings off the bracket that secured them, they would break. Fortunately it was the part of the cord that was being replaced when you install the new O2 sensor. Still, I would like to hear the experience of others. I have to confess putting the couplings on this bracket is challenging.

Thanks again to all for your help.

Hugh

Dear aaallrighty, DJBybee, Klausc, Tooze,

Thank you for your replies. Each of you shared good advice with me. I was going to get the "CEL" scanned first to confirm that I indeed need an O2 sensor. However, thanks to the replies, despite the high mileage the CEL could be caused by a lose gas cap, or leaking vacuum line, etc.

I once saw an old O2 sensor that was replaced on this car or the other '96 850 I have and the sensor looked like a big spark plug. It had screw in threats with an electrical cord that traveled toward the engine compartment.

I'll confirm its definitely an O2 sensor, and if it is, take a shot at repairing it myself.

Question: If the 02 sensor is bad. Once I replace it, with the CEL go off automatically or does it have to be cleared?

Fellas, thank you for your help. God willing I'll be owning these cars for a while, and if I can learn how to make this repair, I'll save myself a boat load of money over the long run.

Hugh

Try this site:


www.matthewsvolvosite.com

First things, first, friend. Like Klaus says, accurate diagnosis is critical, especially for those on a budget. Check engine light can come on for something as benign as a loose fuel filler cap. Which is free to fix. And you can return your fancy wrench and pocket the cash. And the light can come on for literally thousands of reasons besides a bad oxygen sensor. Assume nothing. Need accurate info before you start throwing parts at it.

For being on a budget, you are spending too much money. Check the codes first and clear them. A slow working sensor may not turn on the CEL for a couple of weeks.
Don't forget, air leaks via vacuum lines, intake manifold gasket, and other manifold leaks cause the system to run on the rich side which coats the front O2 sensor and kills it. Fixing the manifold leaks is cheap, and then running the engine hot will clean off the O2 sensor.

The rear O2 sensor does not "follow" the front O2 sensor. It lasts much longer than the front sensor and has it's own codes when it fails.

Check on Volvospeed.com for a pic or 2.

Klaus
--
Proud owner of a 1967 220S. If I had more room, I would have more Volvos.

All I can tell you is dive in. I did it on my 1st 95 850 with regular combo wrenches. You are ahead of the game; you have the right wrench. I just got underneath(AFTER JACK STANDS WERE IN PLACE!)and followed the wires to their respective plugs. Use PB blaster to get the old ones out and make sure to use the goo that comes with the new sensors. You may also want to go a tad to the right and then unscrew the sensors. How did you come to know the O2 sensors needed replacing; yes - 200K miles is a good indicator but you may want to go to Autozone and let them put your brick on their scantool (free). I will be moving the O2 sensors from my old one, which is wrinkled (17 year old daughter + Cherry tree at 55 MPH = Thank God she was in a Volvo), to one I just picked up in Chicagoland and drove to NJ.

If you got plug in oe style replacements..it really cant be any easier..
unplug them both..the connections for which is up near the transmission in the back of the engine close to the firewall.
unscrew them both..the rear one you'll have to remove 4 bolts to take out a flange that is in the way..
take them both out and put the new ones in..do not plug them till after then are in place..
so to summon
take the old ones out..put the new ones in..
no real tricks..and welcome to the enlightened world of DIY car repairs..