1995 855 Stripped rear O2 sensor

lcc014 · Post by **lcc014** » 20 Apr 2015, 08:42

I tried to replace rear O2 sensor due to a A1 code recently logged. Everything went smooth (including cutting off one of the 4 bolts holding the protective plate under rear O2 sensor). When trying to unscrew the old rear O2 sensor with the special socket, it stripped the O2 sensor. I did spray PB blaster onto sensor and let it sit for a while before tackling the sensor.
This is the second time I tried to replace the sensor. Last time was 7 years ago at 187k miles. Now, my car is at 300k miles. I did not install the rear sensor very tight back then and used antisezie compound too. Whenever I tried to unscrew the sensor, the whole exhaust pip went up a bit (anticlockwise). There was not enough leverage to hold the exhaust pipe in place (not moving) while trying to unscrew the sensor with that special socket. After a couple tries, I could see the sensor started to strip a little bit. I stopped trying immediately.
Any idea to tackle this problem and unscrew that sensor ?

Thanks,

Ching-Ho Cheng

Post by **xHeart** » 20 Apr 2015, 09:23

lcc014 wrote:...

When trying to unscrew the old rear O2 sensor with the special socket, it stripped the O2 sensor. I did spray PB blaster onto sensor and let it sit for a while before tackling the sensor.
This is the second time I tried to replace the sensor. Last time was 7 years ago at 187k miles. Now, my car is at 300k miles. I did not install the rear sensor very tight back then and used antisezie compound too...

I recently replace the HO2 sensors - both front and rear.
Roads are salted in this area, so I was preparing and expecting the worst. It is my daily-driver.

After several PB soakings - weekends and overnights - it turned with the 1/2" breaker bar on special socket without much force. Ozark Lee reminds us to apply "gentle and constant pressure" after the socket is fully seated on the sensor. It is 22mm hex.

The crow-foot style socket is best for this job.

Post by **erikv11** » 20 Apr 2015, 09:47

I agree, hit it with penetrant it every night for a week or two then go back in there and try again. Try using heat, that has worked for me.

Post by **mecheng** » 20 Apr 2015, 10:22

If the head is rounded, use a vice grip. Thats what I had to do, with lots of penetrent. I tapped the thread with a hammer so that it soaks in. I destroyed the sensor but I got it out. I used the vice grip on the body of the sensor.

lcc014 · Post by **lcc014** » 20 Apr 2015, 10:24

Thanks for the responses. When soaking with PB Blaster, overnight/days, should I drive the car in between ? How long was the 1/2" breaker bar to be used to unscrew the sensor ? My 1/2" ratchet was about 18" long and I could not unscrew the sensor with it. I use this ratchet all the times for all my jobs in this Volvo. I did try a 24 inches long breaker bar but it was too long under the car. I did not have a lift so car was on ramp and driver side rear wheel was jacked up to get more room.

Post by **xHeart** » 20 Apr 2015, 19:05

lcc014 wrote:Thanks for the responses. When soaking with PB Blaster, overnight/days, should I drive the car in between ? How long was the 1/2" breaker bar to be used to unscrew the sensor ? My 1/2" ratchet was about 18" long and I could not unscrew the sensor with it. I use this ratchet all the times for all my jobs in this Volvo. I did try a 24 inches long breaker bar but it was too long under the car. I did not have a lift so car was on ramp and driver side rear wheel was jacked up to get more room.

Use a seringe to drop few drops at the precise location each night. The wetness will stay after few times. You can drive after overnight.

I do not use extension between socket and breaker bar. Raise the car over jack stands for safety and clearance so you can work from below. Be careful.

Unscrew is turning it counter-clockwise, NOT clockwise.

Disconnecting the wires takes special skills called patience, you may break the connector. Take a closer look at the new connector before embarking on disconnecting old.

Post by **taxi** » 21 Apr 2015, 09:36

Hi!
I recently replaced my cat, and I just have to say, I did nothing gentle. I just put an open wrench on the sensors and hit it as hard as I could with a sledge (couldn't find my hammer) and both oxygen sensors survived the relocation to the new cat!
The front oxygen sensor came loose on the first hit, but the rear one needed about five hits.
Do you really have to be so careful with the sensors?
Car: 2000 V70 (old body)
Cheers!

Post by **JDS60R** » 21 Apr 2015, 09:57

Get a straight metal file and file down the edges of the sensor and install the next size down deep socket ( you may have to cur off the leads. Or, grab some map gas and a good vice grip or a plumbers wrench. heat up the bung (concentrate on the bung not the sensor and turn it orange ( the sensor will also be a dull orange. Then turn it out. ( have fire equipment handy.) Or - buy a cheap 7/8 or 22mm socket and weld it onto the sensor in a few spots. Let the heat soak in while welding. Then turn it out

Post by **JDS60R** » 21 Apr 2015, 13:18

Or mail it to me. I will get it out and send it back to you in 2 days. If its truly bonded I will weld in a new bung for you. Just pay to get it here and back ( and the bung if needed) .

lcc014 · Post by **lcc014** » 21 Apr 2015, 13:55

xHeart wrote:
lcc014 wrote:Thanks for the responses. When soaking with PB Blaster, overnight/days, should I drive the car in between ? How long was the 1/2" breaker bar to be used to unscrew the sensor ? My 1/2" ratchet was about 18" long and I could not unscrew the sensor with it. I use this ratchet all the times for all my jobs in this Volvo. I did try a 24 inches long breaker bar but it was too long under the car. I did not have a lift so car was on ramp and driver side rear wheel was jacked up to get more room.
Use a seringe to drop few drops at the precise location each night. The wetness will stay after few times. You can drive after overnight.

I do not use extension between socket and breaker bar. Raise the car over jack stands for safety and clearance so you can work from below. Be careful.

Unscrew is turning it counter-clockwise, NOT clockwise.

Disconnecting the wires takes special skills called patience, you may break the connector. Take a closer look at the new connector before embarking on disconnecting old.

The special socket that I used was an offset oxygen sensor socket, similar to crowfoot. I have the deep socket type O2 sensor socket. I will try that one next. To unscrew the sensor, I did turn my ratchet Anti-clockwise, not clockwise. I will try to soak it a few night and try again.
Thanks.