Wile E. Coyote

Hello,
I recently bought a 2000 E55 AMG and I need some sage advise from the DIY crowd in the MB forum. I'd like to know if there are any tricks to replacing the upstream (pre-cat) oxygen sensors on my ride. Both of the sensors are bad and need to go bye, bye. Both look very hard to get at from the top. Are they accessible from the bottom? What to do? What to do? Thanks!

Neanicu888

Lots of WD-40 the night before you do it and buy the Mercedes oxygen sensors removal tool from EBay! You can also order the oxygen sensor rethread tool in case you mess things up in there.
Good luck!

Wile E. Coyote

Thanks! It figures that you'd need some special too for this. It's amazing how may ways auto manufactures disregard DIYs and their love of their machines. Sigh......

Wile E. Coyote

Which type of 22 mm O2 sensor socket wrench should I buy? There is a choice between several offset sockets and one that looks like a cutaway spark plug socket. (It looks like the offset sockets might get in the way of themselves.) Also, should I spring for a thread restorer? If so, is the thread on the sensors 18 mm? And, sorry to be a pest, but I'm a newbie AND an **** retentive! ; )

Neanicu888

Here's some help :

http://www.pelicanparts.com/techarti...eplacement.htm

It's not for E55 AMG,but you'll get the idea...

Neanicu888

If you have problems with space using the tool,I would just drop the exhaust. I know it sounds all complicated,but it is not that hard. Having the exhaust on the floor,it would make the removal of oxygen sensors a lot easier,in case they don't want to come out while it's on the car.
I know some members won't agree using this method,but it is up to you...

Peter_02AMG

No special tool required. Just use a open end wrench. I removed my 02 a dozen time in the past fews month.

Wile E. Coyote

Thanks! That was helpful. I hope I never have to resort to dropping the exhaust manifolds. I'm just not set up tool wise and otherwise to undertake that.

ruBENZ

For what it's worth, I just replaced the after cat O2sensor using an open end 17mm wrench. For the pre-cat sensor, begin by loosing (not removing) the old sensor, disconnect the old top end, connect the new top end, secure the old top end to the new sensor via tape, garbage bag tie, shoe lace, etc, remove the old sensor, pull the new sensor thru, and install the new sensor. Good luck.

Wile E. Coyote

That is good wrenching advice and thanks for it! (However, I think you meant a 22mm open end wrench.) I might not have to do that if things go as planned. (After all, I am Wile E. Coyote, so what could possibly go wrong?) I just ordered a 16" socket extension and an O2 sensor socket that looks like a cutout spark plug wrench. I've got an unobstructed shot at the oxygen sensor on the right (passenger) side. However, things aren't so great on the left (driver's) side, but still doable, me thinks. If I can change out the sensors as planned, I'll post my R&R method to the forum.

Neanicu888

Hey Wile E. Coyote,I think you did the right thing by ordering the tool. And let me tell you why...I've seen quite a few sensors that were basically ' welded ' onto the exhaust,rusted,that under any circumstance will come off in one piece. The condition of a sensor might depend on different factors,like if it's ever been changed,the climate where the car has been driven etc.
The scenario you've been described here by others,where they just used a 17 mm open wrench is really ideal and it might work in your case as well,but if it doesn't,it's better to be ready. That's why I've mentioned the removal and rethread tools and even went as far as mentioning dropping the exhaust,as I've seen too many rounded up oxygen sensors bolts,cases where you even had to go as far as using a blow torch on that sucker to get it out.

Anyway,good luck!

Wile E. Coyote

OK, here it is as promised. And as luck would have it, things did go as planned. (Sorta....) The right (passenger) side got changed in about 15 minutes. You DO have a straight at the sensor and need only a 16" extension on a straight, slotted 02 sensor tool. The left (driver) side is not nearly as easy, but is still doable alone and with minimal tools. However, it will go much easier and a lot more quickly if you have some help. Also, plan on spending some time underneath as this really is necessary. You CAN remove the 02 sensor using a 16" extension, however, you CANNOT install one using only the extension! After you have removed your defective sensor, the fun begins. You must first feed the new sensor down between the firewall and the AC line that runs along the firewall rim. (Make sure you don't disturb the anti-seize compound on the new sensor's threads. If your new sensors didn't come with anti-seize compound, you MUST apply some!) Stop feeding it down before you overshoot the sensor hole in the manifold. Now, you must jack up the car and head underneath. (NOTE: Insert common sense into you brain and follow the standard safety procedures regarding working underneath a vehicle NOW!) You must feed the new sensor into the hole and start twisting it into the threading. (Yes, there really is room for you to do this!) Here's where it helps to have a someone helping you topside. The installation works best if that certain someone above you "pre-loads" the sensor's threading process by twisting the cable clockwise about 1 1/2 turns while you hold the sensor in one place. (I was actually able to twist the sensor in about 540 degrees via the cable twisting alone after the threading had been started from the bottom!) After the sensor can no longer be twisted by hand, it's time to use the straight, slotted socket and extension again. The socket alone can and should be placed over the sensor from underneath the car. It is from that vantage point only that you can tell if the socket is properly mated into the hex portion of the sensor. When that's done, lower your 16" extension with an universal joint on the end. It's a little tricky to get the universal joint to plug into the 02 sensor socket, but after a few tries you'll get it into place. Tighten until the new 02 sensor is snug, but DO NOT overtighten. You may have to loosen the socket from the sensor by pushing it up from below. I used a long, flat blade screwdriver. Work the socket, universal and extension up carefully between the AC line and the rim of the firewall and plug the sensor cable in. Done! Smoke 'em if ya got 'em!